fix(install): make Gitea repo install-ready + canonical marketplace flow (#37)

Adds the bits needed for `claude plugin marketplace add
https://git.moleculesai.app/molecule-ai/molecule-mcp-claude-channel.git`
to actually work, and rewrites the README install section to use the
canonical Claude Code marketplace flow (replacing the suspended-GitHub
install command).

Changes:
- New `.claude-plugin/marketplace.json` describing the single-plugin
  marketplace `molecule-channel` with one plugin entry `molecule`.
  Required for `claude plugin marketplace add` to recognize this repo.
- Bump `.claude-plugin/plugin.json` version `0.1.0` → `0.4.0-gitea.1`.
- Bump `package.json` version `0.3.0` → `0.4.0-gitea.1`. (Both versions
  were already drifted; this reconciles them.)
- README install section rewritten:
  - Old: `claude --channels plugin:molecule@Molecule-AI/molecule-mcp-claude-channel`
    (suspended-GitHub URL, no longer resolves)
  - New: `claude plugin marketplace add https://git.moleculesai.app/...`
    + `claude plugin install molecule@molecule-channel` (canonical
    marketplace flow per Claude Code docs)
- README "Contributing" issues link migrated github.com → Gitea.
- Migration note for users on the old install path: GitHub
  Molecule-AI org permanently gone 2026-05-06; new path is direct
  replacement, behavior unchanged.

Version `0.4.0-gitea.1` admits the lineage gap with the
never-recovered-from-GitHub `v0.4.x` work; preserves user expectation
of a 0.4.x release. Annotated tag to follow this PR (re-tag is cheap if
Hongming prefers a different version).

Refs: molecule-ai/internal#37, molecule-ai/internal#38

.claude-plugin/marketplace.json

@@ -0,0 +1,25 @@
+{
+  "name": "molecule-channel",
+  "owner": {
+    "name": "Molecule AI",
+    "email": "support@moleculesai.app",
+    "url": "https://moleculesai.app"
+  },
+  "plugins": [
+    {
+      "name": "molecule",
+      "source": ".",
+      "description": "Bridges Molecule A2A traffic into a Claude Code session via MCP. Subscribe to one or more Molecule workspaces; A2A messages from peers surface as conversation turns; replies route back through Molecule's A2A endpoints.",
+      "version": "0.4.0-gitea.1",
+      "homepage": "https://git.moleculesai.app/molecule-ai/molecule-mcp-claude-channel",
+      "license": "Apache-2.0",
+      "keywords": [
+        "molecule",
+        "molecule-ai",
+        "a2a",
+        "channel",
+        "mcp"
+      ]
+    }
+  ]
+}

.claude-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "molecule",
   "description": "Molecule AI channel for Claude Code — bridges Molecule A2A traffic into a Claude Code session via MCP. Subscribe to one or more Molecule workspaces; A2A messages from peers surface as conversation turns; replies route back through Molecule's A2A endpoints.",
-  "version": "0.1.0",
+  "version": "0.4.0-gitea.1",
   "keywords": [
     "molecule",
     "molecule-ai",

README.md

@@ -16,10 +16,22 @@ No tunnel. No public endpoint. The plugin self-registers each watched workspace
 
 ## Install
 
+This plugin distributes through the Claude Code marketplace flow. From any shell:
+
 ```bash
-claude --channels plugin:molecule@Molecule-AI/molecule-mcp-claude-channel
+# 1. Add the marketplace (one-time per machine)
+claude plugin marketplace add https://git.moleculesai.app/molecule-ai/molecule-mcp-claude-channel.git
+
+# 2. Install the plugin
+claude plugin install molecule@molecule-channel
 ```
 
+`molecule` is the plugin name (from `.claude-plugin/plugin.json`); `molecule-channel` is the marketplace name (from `.claude-plugin/marketplace.json`). Both live in the same repo — installing the marketplace makes the plugin available; installing the plugin enables it for your sessions.
+
+To pin a specific version, append `#<tag>` to the marketplace URL — for example `…/molecule-mcp-claude-channel.git#v0.4.0-gitea.1`. Without a ref, you track `main`.
+
+> **Note for users coming from the GitHub install path**: the GitHub `Molecule-AI` org was suspended on 2026-05-06 and is permanently gone. The earlier `claude --channels plugin:molecule@Molecule-AI/...` invocation no longer resolves. The new path (above) is the canonical replacement; behavior is unchanged.
+
 On first launch the plugin creates `~/.claude/channels/molecule/` and exits with a config-missing error pointing at `.env`. Fill it in:
 
 ```
@@ -43,9 +55,11 @@ The `.env` file is `chmod 600` after first read; tokens never appear in environm
 Re-launch Claude Code:
 
 ```bash
-claude --channels plugin:molecule@Molecule-AI/molecule-mcp-claude-channel
+claude
 ```
 
+(After the one-time `marketplace add` + `plugin install` above, the plugin loads automatically on every `claude` invocation; no per-launch flag needed.)
+
 You should see on stderr:
 
 ```
@@ -142,7 +156,7 @@ A2A messages can carry `Part` entries with `url` and `media_type`. The MVP deliv
 
 ## Contributing
 
-Single-file MCP server. The whole bridge lives in `server.ts`. Open issues at [Molecule-AI/molecule-mcp-claude-channel](https://github.com/Molecule-AI/molecule-mcp-claude-channel/issues).
+Single-file MCP server. The whole bridge lives in `server.ts`. Open issues at [molecule-ai/molecule-mcp-claude-channel](https://git.moleculesai.app/molecule-ai/molecule-mcp-claude-channel/issues).
 
 ## License
 

package.json

@@ -1,6 +1,6 @@
 {
   "name": "molecule-mcp-claude-channel",
-  "version": "0.3.0",
+  "version": "0.4.0-gitea.1",
   "description": "Molecule AI channel for Claude Code — bridges A2A traffic into a Claude Code session via MCP",
   "license": "Apache-2.0",
   "type": "module",