feat: add category and effect as first-class fields in extension schema (#2899)

* feat: add category and effect as first-class fields in extension schema

Add `category` and `effect` as optional fields in the extension schema
(`extension.yml`) and community catalog (`catalog.community.json`).

Schema changes:
- Valid categories: docs, code, process, integration, visibility
- Valid effects: read-only, read-write
- Both fields are optional (backward-compatible with existing extensions)
- Validation raises ValidationError for invalid values when present

Propagation:
- Added `category` and `effect` to all 108 entries in catalog.community.json
  (populated from the existing docs/community/extensions.md table)
- Updated extension template with commented category/effect fields
- Updated add-community-extension skill with new JSON template fields
- Updated `specify extension info` CLI output to display category/effect
- Added properties to ExtensionManifest class

Tests:
- test_valid_category: all 5 category values pass
- test_valid_effect: both effect values pass
- test_invalid_category: invalid value raises ValidationError
- test_invalid_effect: invalid value raises ValidationError
- test_category_and_effect_optional: omitting fields still works

Closes #2874

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix: make category free-form, keep effect validated

Category is a free-form string (only validated as non-empty when present),
while effect remains restricted to 'read-only' or 'read-write'.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix: address PR review feedback

- Add type guard before 'in' check for effect to prevent TypeError on
  unhashable YAML values (list/dict)
- Comment out category/effect in template so authors must opt in
- Use VALID_EFFECTS constant in test instead of hard-coded values

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix: update category docstring to reflect free-form semantics

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* docs: clarify canonical extension effect values

---------

Co-authored-by: Manfred Riem <mnriem@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

.github/skills/add-community-extension/SKILL.md

@@ -70,6 +70,8 @@ Use the existing entries as the format template. Required fields:
     "documentation": "<documentation>",
     "changelog": "<changelog>",
     "license": "<license>",
+    "category": "<category>",
+    "effect": "<effect>",
     "requires": {
       "speckit_version": "<speckit_version>"
     },
@@ -87,6 +89,9 @@ Use the existing entries as the format template. Required fields:
 }
 ```
 
+**Category** — free-form string; common values: `docs`, `code`, `process`, `integration`, `visibility`
+**Effect** — one of: `read-only`, `read-write`
+
 If the extension has optional tool dependencies, add a `"tools"` array inside `"requires"`:
 
 ```json
@@ -113,8 +118,8 @@ Determine the category and effect from the extension's behavior:
 | <Name> | <Description> | `<category>` | <Effect> | [<repo-name>](<repository-url>) |
 ```
 
-**Category** — one of: `docs`, `code`, `process`, `integration`, `visibility`
-**Effect** — `Read-only` (produces reports only) or `Read+Write` (modifies project files)
+**Category** — free-form; common values: `docs`, `code`, `process`, `integration`, `visibility`
+**Effect** — write canonical values `read-only` or `read-write` in `extension.yml` and `catalog.community.json`; use `Read-only`/`Read+Write` only for the docs table display
 
 ### 6. Commit, push, and open PR