Fix doc cross-links for the hierarchy; add package-path + shape gates

Merge brought in the RFC-classification reorg and two new doc gates;
rewrite every drifted packages/<name> cross-link (Markdown link targets,
moved-README relative depths, and .ts comment paths) to the grouped paths.

Add two doc-sync/hygiene gates so the manual checks this restructure
needed become automated:
- verify-package-paths.ts: flags a packages/<path> reference (in Markdown
  or a .ts comment/string) that does not resolve AND names a real package
  in a segment — i.e. a stale path to a MOVED package. A path naming a
  non-existent package (a forward-looking proposal) is left alone, so it
  applies uniformly across proposed/implemented/rejected.
- check-workspace-constraints: assert the packages/<group>/<pkg> depth-2
  shape (group dirs carry no package.json; no flat or over-nested
  packages). Group names stay open; only the shape is fixed.

packages/support/llm-replay/src/index.ts

@@ -10,7 +10,7 @@
  * The fixture IS the persisted session log (`<scenario>/session.jsonl`): its
  * `assistant/chunk` events carry every {@link StreamChunk}, so grouping them by
  * `(turn, step)` reconstructs each `stream()` call's chunk sequence (one model
- * call per loop step — see packages/agent-loop/src/loop.ts). Recording is
+ * call per loop step — see packages/core/agent-loop/src/loop.ts). Recording is
  * therefore "run the real agent once and harvest the `.jsonl`", done by the
  * snapshot harness — this plugin does not record.
  *
@@ -46,7 +46,7 @@ import { LlmError, assertNever } from '@deepseek-ai/dsh-llm'
  * so it can faithfully replay BOTH branches of the documented LLM failure
  * contract — an adapter may THROW from `stream()` or end with a `finish` error
  * chunk — plus a `hang` marker for cancellation scenarios (mirrors the
- * `MockAdapter` `hang` support in packages/agent-loop/tests).
+ * `MockAdapter` `hang` support in packages/core/agent-loop/tests).
  *
  * A `throw` entry carries any `chunks` the adapter emitted BEFORE it threw, so
  * a mid-stream transport failure (partial output then `STREAM_CLOSED`) replays