#46 (SLICE-3, accept): Accept all pending proposals in one gesture

Document-edit flow SLICE-3 — completes reach→review→accept
(specs/coauthoring-document-edit-flow.md §7.2, INV-42). A single "Accept all"
gesture applies every pending proposal on the current document through the
existing F4 acceptById seam (block proposals take the INV-40 word-precise path
automatically), in descending anchor order so an earlier accept never invalidates
a later one, skipping (never force-applying) proposals that can't anchor and
reporting applied-vs-skipped. Batched application of the existing accept path — no
new mechanism; the webview posts intent only (INV-35). No confirmation dialog
(undo restores).

- proposalController.ts: acceptAllProposals(document) → {applied, skipped}
  (descending order, orphan-skip); accept/acceptById gain a silent opt so the
  batch suppresses N per-proposal orphan warnings in favour of one report.
- trackChangesPreview.ts: ToolbarMsg += {type:"acceptAll"}; handleWebviewMessage
  routes it to a public acceptAll(document) that batches + reports.
- extension.ts + package.json: cowriting.acceptAllProposals command (active doc,
  markdown-gated palette entry) for the non-webview path.
- media/preview.ts + shellHtml: "✓✓ Accept all" toolbar button, posting the
  intent, shown only with ≥2 pending proposals (authorable, on-state).
- trackChangesModel.ts: diffToBlockHunks now emits one block-aligned hunk per
  CHANGED block even when changed blocks are ADJACENT (treats changed blocks as
  1:1 anchors alongside unchanged ones; gap-spans only cover add/remove runs
  between anchors) — fixes adjacent changed blocks collapsing into one proposal.
- f12Accept host E2E (apply-all reconstructs; orphan skip + report; single
  proposal; command registered/gated); MANUAL-SMOKE-F12 §3.

214 unit + 73/5 host E2E green. Completes the document-edit-flow cluster
(#42 reach + #47 review + #46 accept).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

package.json

@@ -83,6 +83,11 @@
         "command": "cowriting.editDocument",
         "title": "Ask Claude to Edit Document",
         "category": "Cowriting"
+      },
+      {
+        "command": "cowriting.acceptAllProposals",
+        "title": "Accept All Claude Proposals",
+        "category": "Cowriting"
       }
     ],
     "menus": {
@@ -110,6 +115,10 @@
         {
           "command": "cowriting.editDocument",
           "when": "editorLangId == markdown"
+        },
+        {
+          "command": "cowriting.acceptAllProposals",
+          "when": "editorLangId == markdown"
         }
       ],
       "editor/title": [