P2 redesign · phase 2.5: tasks.md rewrite + UI patch-up

The store rewrite in e7eea7a left tasks.md describing a data shape
(fat schedules, host.repo_initialised_at, manual flag) that no longer
exists, and left the host-detail templates rendering against fields
the store no longer exposes. This commit reconciles both.

tasks.md
* Mid-phase pivot called out at the top of Phase 2 with commit hashes.
* P2-01..P2-05 kept as done but stamped ⚠️ "shipped against old shape
  — to re-validate under P2R-02".
* P2-04.5 (manual flag) struck as superseded.
* New P2R-NN section covering work that previously lived only in
  commit messages and code stubs:
    P2R-00.1/00.2/00.3/00.4 — phases already shipped (this commit
                              records 00.4)
    P2R-01 — REST + WS rewire against slim schedules + source groups
             + repo maintenance + auto-init
    P2R-02 — UI rewire against the v4 wireframes
    P2R-03..05 — prune / check / unlock command surfaces
    P2R-06 — server-side maintenance ticker (cadence-driven)
    P2R-07 — repo stats panel
    P2R-08 — pending_runs queue worker
    P2R-09 — auto-init UX polish
    P2R-10..12 — pre/post hooks rehomed from schedule onto source group
    P2R-13..14 — bandwidth + next/last-run surface
* P2-16/17/18 (Windows + announce-and-approve) untouched.
* Phase 2 acceptance criteria rewritten against the new model.

UI patch-up (P2R-00.4)
* host_detail.html + host_row.html: removed every $host.RepoInitialisedAt
  reference (column dropped in migration 0008 — render was 500'ing).
* Removed manual init-repo branches; the auto-init path replaces them.
* Schedules sub-tab demoted from active link to inert div until P2R-02
  rebuilds the page (it was linking to a raw 501 from the stubbed
  ui_schedules.go handlers).
* Disabled the four per-host Run-now buttons (dashboard row + host
  detail header + empty-snapshots state + right-rail) with a
  "lands in P2 Phase 4" hint — handler is 501-stubbed pending P2R-01,
  so leaving them clickable produced silent failures over htmx.
* Dashboard row-action becomes "Open →" instead of Run-now.

Project tooling
* .mcp.json at repo root: project-scoped Playwright MCP override.
  Forces --headless (so I don't pop a browser at the operator) and
  --output-dir _diag (so screenshots / traces land in the gitignored
  _diag/ directory rather than scattered at the repo root).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/templates/partials/host_row.html

@@ -51,22 +51,8 @@
       <span class="mono text-xs text-ink-fade">offline</span>
     {{- else if .CurrentJobID -}}
       <a href="/jobs/{{deref .CurrentJobID}}" class="btn btn-ghost">View job →</a>
-    {{- else if not .RepoInitialisedAt -}}
-      <button class="btn btn-danger"
-              hx-post="/hosts/{{.ID}}/init-repo"
-              hx-swap="none"
-              hx-disabled-elt="this"
-              title="restic repo not yet initialised">Init repo</button>
-    {{- else if eq (deref .LastBackupStatus) "failed" -}}
-      <button class="btn"
-              hx-post="/hosts/{{.ID}}/run-backup"
-              hx-swap="none"
-              hx-disabled-elt="this">Retry</button>
     {{- else -}}
-      <button class="btn whitespace-nowrap"
-              hx-post="/hosts/{{.ID}}/run-backup"
-              hx-swap="none"
-              hx-disabled-elt="this">Run&nbsp;now</button>
+      <a href="/hosts/{{.ID}}" class="btn btn-ghost whitespace-nowrap" title="per-source-group Run-now lands in P2 Phase 4 — open the host">Open →</a>
     {{- end -}}
   </div>
 </div>