feat: add Firebender integration (Android Studio / IntelliJ) (#3077)

* feat: add Firebender integration (Android Studio / IntelliJ)

Firebender (https://firebender.com/) is an AI coding agent for Android
Studio and IntelliJ. It reads project-local custom slash commands from
.firebender/commands/*.mdc and project rules from .firebender/rules/*.mdc.

Add a FirebenderIntegration (MarkdownIntegration) that installs the
speckit command templates as .mdc command files and writes the managed
context section into .firebender/rules/specify-rules.mdc. command_filename
is overridden so init-time commands also use the .mdc extension Firebender
requires. Register it in the integration registry, add the catalog entry
and docs row, and add an integration test covering the .mdc command output.

Closes #1548

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* feat: address review - bump catalog updated_at and list firebender as multi-install safe

Bump the catalog top-level updated_at to reflect the new entry, and add firebender (with its .firebender/commands + .firebender/rules/specify-rules.mdc isolation paths) to the 'currently declared multi-install safe integrations' table in the docs.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

integrations/catalog.json

@@ -1,6 +1,6 @@
 {
   "schema_version": "1.0",
-  "updated_at": "2026-06-02T00:00:00Z",
+  "updated_at": "2026-06-22T00:00:00Z",
   "catalog_url": "https://raw.githubusercontent.com/github/spec-kit/main/integrations/catalog.json",
   "integrations": {
     "claude": {
@@ -102,6 +102,15 @@
       "repository": "https://github.com/github/spec-kit",
       "tags": ["cli"]
     },
+    "firebender": {
+      "id": "firebender",
+      "name": "Firebender",
+      "version": "1.0.0",
+      "description": "Firebender IDE integration for Android Studio / IntelliJ",
+      "author": "spec-kit-core",
+      "repository": "https://github.com/github/spec-kit",
+      "tags": ["ide"]
+    },
     "forge": {
       "id": "forge",
       "name": "Forge",