docs(skills): cite PLATFORM_CAPABILITY_TOKENS instead of restating its count

The `requires:` section of `skills/objectstack-platform/SKILL.md` copied two
numbers out of the platform capability vocabulary into prose — "the other
eight tokens" and "the authoritative list of all 28" — and no gate reads
either against `packages/spec/src/kernel/platform-capabilities.ts`. The
vocabulary is 29 on `main` since `package-registry` landed, so both
sentences are already false.

Cite the constant instead. The tokens outside the CLI's `CAPABILITY_PROVIDERS`
map are named as "the tokens in `PLATFORM_CAPABILITY_TOKENS` not in that map",
and the authority sentence keeps the constant and drops the count. The
enumeration under it is unchanged: every name it lists is still in the
constant. Nothing in the tree read the removed numbers, so no gate or
generator follows.

Claude-Session: https://claude.ai/code/session_01Gqi43smmqjJ5sUrhfoPeKu

Co-authored-by: Claude <noreply@anthropic.com>

Author: os-justin

skills/objectstack-platform/SKILL.md

@@ -449,8 +449,8 @@ token through the `CAPABILITY_PROVIDERS` registry in
 | `mcp` | `@objectstack/mcp` |
 | `triggers` | `@objectstack/trigger-record-change`, plus `trigger-schedule` and `trigger-api`. **Pair it with `job`** — schedule and time-relative triggers run on the job service |
 
-The other eight tokens in the vocabulary are **not** in that map and do not
-resolve through it:
+The tokens in `PLATFORM_CAPABILITY_TOKENS` not in that map do not resolve
+through it:
 
 - **Tier-gated** — `ai`, `ai-studio`, `i18n`, `ui`, `auth` have no provider
   entry; dedicated blocks in `serve.ts` `run()` open their tier instead
@@ -460,7 +460,7 @@ resolve through it:
   ships in `@objectstack/security-enterprise`, loaded through `plugins[]`;
   `ai-seat` and `governance` are resolved only by cloud's objectos-runtime.
 
-The authoritative list of all 28 is `PLATFORM_CAPABILITY_TOKENS`
+The authoritative list is `PLATFORM_CAPABILITY_TOKENS`
 (`@objectstack/spec`, `kernel/platform-capabilities.ts`) — an unknown token is
 **rejected by `defineStack` at authoring time**, not at boot.