enh(#2904): add a reviewer entry type so third-party reviewer lanes are discoverable (#2912)

* feat(#2904): add a `reviewer` entry type so third-party reviewer lanes are discoverable

ADR-2782 made a reviewer lane installable by a third party, but neither
discoverability catalog could hold one. The Community Capability Registry
requires a non-empty `loopExtensionPoints` and forbids a lane from declaring
any hook kind, so a `role: "reviewer"` entry is unsatisfiable by construction;
the EoS Registry is for ADR-1239 host integrations, which a lane is not.

Adds a third catalog — `docs/registries/reviewers.json` →
`docs/registries/reviewer-registry.md` — whose `interactions` describes the
lane: slug, flags, transport, evidenceClass, reviewsSection, requiresBinaries,
configKeys, runtimeCompat.

The lane vocabulary is a hand-written mirror of `capability-validator.cjs`
(the same pattern as `AXES` mirroring `HOST_INTEGRATION_AXES`), with parity
enforced by tests/registry-reviewer-parity.test.cjs. `slug` deliberately uses
the runtime `LANE_SLUG_RE` grammar rather than the registry's kebab-only `id`
rule, so real lanes (`lm_studio`, `4o-mini`) are not rejected.

Two binary type branches became three-way Map dispatch. Both now fail loudly
on an unrecognized type instead of silently treating it as a capability —
`renderMarkdown` in particular writes a committed catalog file, so a silent
wrong-title render was the worst failure mode available.

Also fixed while here: `gen-registry.cjs` parsed source JSON with no error
handling, so a malformed or non-array `capabilities.json` surfaced as a raw
SyntaxError/TypeError instead of an actionable CLI error.

Closes #2904

* fix(#2904): bound and sanitize untrusted registry `interactions` strings

Review findings from the pre-PR passes.

Security (isolated pass): `interactions` string fields reached the generated,
committed Markdown catalog with no control-character check and no length
bound. A `reviewsSection` carrying ESC and a `requiresBinaries` element
carrying NUL plus 5000 characters validated clean and landed verbatim in the
rendered page — `mdInline` escapes Markdown metacharacters and collapses CRLF,
but nothing else. The identical gap already existed on the capability type's
`configKeys`/`requires`/`runtimeCompat`/`produces`/`consumes`, so it is fixed
there too rather than inherited into a third type.

`hasDisallowedControlChar` is lifted to module scope so exactly one
implementation exists, and a shared `validateStringArrayField` enforces
control-character rejection, a 200-character element cap and a 50-element
array cap for both types.

Correctness (standards pass): `renderMarkdown`'s per-entry summary builder was
still an if/else-if chain whose final `else` was the capability branch — the
one per-type dispatch point this change had not converted, and the same silent
fallthrough it removes elsewhere. It now lives in `RENDER_META` alongside the
title, so a fourth type cannot silently inherit capability's rendering. All
three types' rendered output is byte-identical to before the refactor.

Also corrects a test comment that still claimed the reviewer suites were
failing-first against an unmodified module.

* chore(#2904): backfill changeset PR number (#2912)

.github/PULL_REQUEST_TEMPLATE/registry-entry.md

@@ -15,6 +15,7 @@ Full schema and process: [docs/registries/README.md](../../docs/registries/READM
 
 - [ ] Capability Registry entry — adds/updates one object in `docs/registries/capabilities.json`
 - [ ] EoS Registry entry — adds/updates one object in `docs/registries/eos.json`
+- [ ] Reviewer Lane Registry entry — adds/updates one object in `docs/registries/reviewers.json`
 
 ## The entry
 
@@ -44,6 +45,7 @@ Full schema and process: [docs/registries/README.md](../../docs/registries/READM
 - [ ] `id`, `name`, `type`, `repo`, `description`, `author`, `license`, `enginesGsd`, `install`, `uninstall`, `interactions`, `discussion` are all present and non-empty
 - [ ] **(Capability entries only)** `interactions.loopExtensionPoints` is a non-empty subset of the 12 Loop Extension Points, `interactions.hookKinds` ⊆ `{step, contribution, gate}`, and `interactions.configKeys` / `requires` / `runtimeCompat` / `produces` / `consumes` are present (empty arrays are fine where nothing applies)
 - [ ] **(EoS entries only)** `protocolVersion` is an integer ≥ 1, `interactions.interfacePoints` is a non-empty subset of the six interface points, `interactions.profile` is one of `programmatic-cli` / `declarative-cli` / `ide`, and `interactions.axes` has exactly the eight required axis keys plus, optionally, `effortSurface` (`argv` / `none`)
+- [ ] **(Reviewer entries only)** `interactions.slug` matches the lane slug grammar `^[a-z0-9][a-z0-9_-]*$`, `interactions.flags` is a non-empty array matching `^--[a-z0-9][a-z0-9-]*$`, `interactions.transport` is `spawn` or `openai-http`, `interactions.evidenceClass` is `source-grounded` or `diff-only`, `interactions.reviewsSection` is a non-empty string (max 200 characters), and `interactions.requiresBinaries` / `configKeys` / `runtimeCompat` are present (empty arrays are fine where nothing applies)
 
 ## Ownership & non-endorsement
 
@@ -53,12 +55,12 @@ Full schema and process: [docs/registries/README.md](../../docs/registries/READM
 
 ## One entry, one PR
 
-- [ ] This PR adds or updates exactly **one** entry, in exactly one of `capabilities.json` / `eos.json`
+- [ ] This PR adds or updates exactly **one** entry, in exactly one of `capabilities.json` / `eos.json` / `reviewers.json`
 - [ ] I have not bundled any other registry entry, code change, or unrelated docs change into this PR
 
 ## Generated file in sync
 
-- [ ] I ran `npm run gen:registry` after editing the JSON source, and this PR includes the regenerated `docs/registries/capability-registry.md` or `docs/registries/eos-registry.md`
+- [ ] I ran `npm run gen:registry` after editing the JSON source, and this PR includes the regenerated `docs/registries/capability-registry.md`, `docs/registries/eos-registry.md`, or `docs/registries/reviewer-registry.md`
 - [ ] I did **not** hand-edit the generated `.md` file directly — all edits were made to the JSON source
 
 ## Documentation