Rename "channels" to "conversations."

The term "channel" for a conversational container has a long and storied history, but is mostly evocative of IRC and of other, ah, "nerd-centric" services. It does show up in more widespread contexts: Discord and Slack both refer to their primary conversational containers as "channels," for example. However, I think it's unnecessary jargon, and I'd like to do away with it.

To that end, this change pervasively changes one term to the other wherever it appears, with the following exceptions:

* A `channel` concept (unrelated to conversations) is also provided by an external library; we can't and shouldn't try to rename that.
* The code to deal with the `pilcrow:channelData` and `pilcrow:lastActiveChannel` local storage properties is still present, to migrate existing data to new keys. It will be removed in a later change.

This is a **breaking API change**. As we are not yet managing any API compatibility promises, this is formally not an issue, but it is something to be aware of practically. The major API changes are:

* Paths beginning with `/api/channels` are now under `/api/conversations`, without other modifications.
* Fields labelled with `channel…` terms are now labelled with `conversation…` terms. For example, a `message` `sent` event is now sent to a `conversation`, not a `channel`.

This is also a **breaking UI change**. Specifically, any saved paths for `/ch/CHANNELID` will now lead to a 404. The corresponding paths are `/c/CONVERSATIONID`. While I've made an effort to migrate the location of stored data, I have not tried to provide adapters to fix this specific issue, because the disruption is short-lived and very easily addressed by opening a channel in the client UI.

This change is obnoxiously large and difficult to review, for which I apologize. If this shows up in `git annotate`, please forgive me. These kinds of renamings are hard to carry out without a major disruption, especially when the concept ("channel" in this case) is used so pervasively throughout the system.

I think it's worth making this change that pervasively so that we don't have an indefinitely-long tail of "well, it's a conversation in the docs, but the table is called `channel` for historical reasons" type issues.

Merges conversations-not-channels into main.

3 files changed, 24 insertions, 24 deletions

diff --git a/ui/lib/state/remote/channels.svelte.js b/ui/lib/state/remote/conversations.svelte.js
index 1e40075..79868f4 100644
--- a/ui/lib/state/remote/channels.svelte.js
+++ b/ui/lib/state/remote/conversations.svelte.js
@@ -1,8 +1,8 @@
 import { DateTime } from 'luxon';
 
-class Channel {
+class Conversation {
   static boot({ at, id, name }) {
-    return new Channel({
+    return new Conversation({
       at: DateTime.fromISO(at),
       id,
       name,
@@ -16,14 +16,14 @@ class Channel {
   }
 }
 
-export class Channels {
+export class Conversations {
   all = $state([]);
 
   add({ at, id, name }) {
-    this.all.push(Channel.boot({ at, id, name }));
+    this.all.push(Conversation.boot({ at, id, name }));
   }
 
   remove(id) {
-    this.all = this.all.filter((channel) => channel.id !== id);
+    this.all = this.all.filter((conversation) => conversation.id !== id);
   }
 }
diff --git a/ui/lib/state/remote/messages.svelte.js b/ui/lib/state/remote/messages.svelte.js
index 1be001b..852f29e 100644
--- a/ui/lib/state/remote/messages.svelte.js
+++ b/ui/lib/state/remote/messages.svelte.js
@@ -2,21 +2,21 @@ import { DateTime } from 'luxon';
 import { render } from '$lib/markdown.js';
 
 class Message {
-  static boot({ id, at, channel, sender, body }) {
+  static boot({ id, at, conversation, sender, body }) {
     return new Message({
       id,
       at: DateTime.fromISO(at),
-      channel,
+      conversation,
       sender,
       body,
       renderedBody: render(body),
     });
   }
 
-  constructor({ id, at, channel, sender, body, renderedBody }) {
+  constructor({ id, at, conversation, sender, body, renderedBody }) {
     this.id = id;
     this.at = at;
-    this.channel = channel;
+    this.conversation = conversation;
     this.sender = sender;
     this.body = body;
     this.renderedBody = renderedBody;
@@ -26,8 +26,8 @@ class Message {
 export class Messages {
   all = $state([]);
 
-  add({ id, at, channel, sender, body }) {
-    const message = Message.boot({ id, at, channel, sender, body });
+  add({ id, at, conversation, sender, body }) {
+    const message = Message.boot({ id, at, conversation, sender, body });
     this.all.push(message);
   }
 
diff --git a/ui/lib/state/remote/state.svelte.js b/ui/lib/state/remote/state.svelte.js
index fb46489..3d65e4a 100644
--- a/ui/lib/state/remote/state.svelte.js
+++ b/ui/lib/state/remote/state.svelte.js
@@ -1,11 +1,11 @@
 import { User, Users } from './users.svelte.js';
-import { Channels } from './channels.svelte.js';
+import { Conversations } from './conversations.svelte.js';
 import { Messages } from './messages.svelte.js';
 
 export class State {
   currentUser = $state();
   users = $state(new Users());
-  channels = $state(new Channels());
+  conversations = $state(new Conversations());
   messages = $state(new Messages());
 
   static boot({ currentUser, heartbeat, resumePoint, events }) {
@@ -30,8 +30,8 @@ export class State {
     // Heartbeats are actually completely ignored here. They're handled in `Session`, but not as a
     // special case; _any_ event is a heartbeat event.
     switch (event.type) {
-      case 'channel':
-        return this.onChannelEvent(event);
+      case 'conversation':
+        return this.onConversationEvent(event);
       case 'user':
         return this.onUserEvent(event);
       case 'message':
@@ -39,23 +39,23 @@ export class State {
     }
   }
 
-  onChannelEvent(event) {
+  onConversationEvent(event) {
     switch (event.event) {
       case 'created':
-        return this.onChannelCreated(event);
+        return this.onConversationCreated(event);
       case 'deleted':
-        return this.onChannelDeleted(event);
+        return this.onConversationDeleted(event);
     }
   }
 
-  onChannelCreated(event) {
+  onConversationCreated(event) {
     const { id, name } = event;
-    this.channels.add({ id, name });
+    this.conversations.add({ id, name });
   }
 
-  onChannelDeleted(event) {
+  onConversationDeleted(event) {
     const { id } = event;
-    this.channels.remove(id);
+    this.conversations.remove(id);
   }
 
   onUserEvent(event) {
@@ -80,8 +80,8 @@ export class State {
   }
 
   onMessageSent(event) {
-    const { id, at, channel, sender, body } = event;
-    this.messages.add({ id, at, channel, sender, body });
+    const { id, at, conversation, sender, body } = event;
+    this.messages.add({ id, at, conversation, sender, body });
   }
 
   onMessageDeleted(event) {