Phase 1: mechanical echo→chorus rename with back-compat shims

Identity rename, no behavior change (CHORUS-PLAN.md Phase 1):
- Plugin echo-memory → chorus-memory: manifest (v2.0.0-alpha.1), skill dir,
  16 scripts (chorus.py, chorus_config.py, …), EchoError → ChorusError,
  /chorus-* commands, hook paths, docs, scaffold seeds, eval harness,
  build.py. Docs endpoint → chorusapi.mpm.to.
- Env ECHO_* → CHORUS_*; config → ~/.claude/chorus-memory/config.json;
  state dir → ~/.chorus-memory/; marker → _agent/chorus-vault.md.

Back-compat shims (one major version):
- chorus_config aliases legacy ECHO_* env at import; reads a legacy
  echo-memory config.json when no CHORUS config exists (writes never
  land there); doctor/config report the legacy source.
- State dir honors an existing ~/.echo-memory when the new dir is absent
  (offline queue not stranded).
- Marker dual-probe in load/doctor/bootstrap/lint/sweep/migrate: a
  pre-fork _agent/echo-vault.md counts as bootstrapped; bootstrap repair
  won't write a second marker; routing gains agent-marker-legacy (GET).

Verified: 25/25 unit tests, scaffold + routing-sync checks, 4 mock e2e
suites, run_eval metrics unchanged, +6 shim smoke tests green.
Rebuilt chorus-memory.plugin (79 entries).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

chorus-memory.plugin.src/commands/chorus-doctor.md

@@ -0,0 +1,20 @@
+---
+description: Check CHORUS readiness — Python, vault reachability, auth, bootstrap/schema, and key source
+---
+
+Use the **chorus-memory** skill to run a one-call readiness check before relying on memory.
+
+```bash
+CHORUS="${CLAUDE_PLUGIN_ROOT}/skills/chorus-memory/scripts/chorus.py"
+[ -f "$CHORUS" ] || CHORUS=$(ls /sessions/*/mnt/.remote-plugins/*/skills/chorus-memory/scripts/chorus.py 2>/dev/null | head -1)   # CoWork sandbox fallback
+python3 "$CHORUS" doctor
+# Windows: use `python` or `py -3` if `python3` is not on PATH.
+```
+
+It prints green/red for: Python version, vault reachability, auth accepted, vault
+bootstrapped (+ `schema_version`), and the **config source** for owner/endpoint/key
+(per-field: env override `CHORUS_OWNER`/`CHORUS_BASE`/`CHORUS_KEY`, then the machine-local
+`~/.claude/chorus-memory/config.json` — or `baked-in (plugin)` on a per-user baked build,
+which is authoritative and reported as such). Exits non-zero if anything is red — if the config is
+missing (or still the placeholder template), ask the operator for their chorus-memory config file and install it with `chorus.py config import <path>` (or `config set --owner … --endpoint … --key …`). For the full vault-invariant lint, run
+`/chorus-health`.