fix(context): sync to the estate canonical context-sync.sh, drop Cursor/Aider

This repo's copy of context-sync.sh was two days stale against the version
Mathias's Cursor/Aider decision (2026-09-01) already landed in dma-cli:
still generated .cursorrules and .aider.conventions.md, and lacked the
--force/placeholder pre-flight and .context/mcp.json root-merge dma-cli's
copy has had since.

Found while building the estate-wide context-sync drift gate (ADR-0019) --
this is exactly the drift the gate exists to catch, found by hand while
establishing the baseline it will check going forward.

- script synced to the canonical hash (dma-cli's current copy)
- .cursorrules, .aider.conventions.md, .aider.conf.yml deleted
- Taskfile's drift assertion and file list narrowed to match
- AGENTS.md, .context/system-prompt.txt regenerated against canonical

task check -> exit 0.

Taskfile.yml

@@ -27,12 +27,12 @@ tasks:
             echo "✓ context sync: skipped in CI"
           else
             bash scripts/context-sync.sh
-            drift=$(git status --porcelain -- AGENTS.md CLAUDE.md .cursorrules .aider.conventions.md .context/system-prompt.txt 2>/dev/null)
+            drift=$(git status --porcelain -- AGENTS.md CLAUDE.md .context/system-prompt.txt 2>/dev/null)
             if [ -n "$drift" ]; then
               echo "ERROR: derived adapters drifted from canonical context." >&2
               echo "$drift" >&2
               echo "" >&2
-              echo "Run: git add AGENTS.md CLAUDE.md .cursorrules .aider.conventions.md .context/system-prompt.txt" >&2
+              echo "Run: git add AGENTS.md CLAUDE.md .context/system-prompt.txt" >&2
               echo "     git commit -m 'chore: re-sync context adapters'" >&2
               exit 1
             fi
@@ -58,5 +58,3 @@ tasks:
     cmds: [bash scripts/context-sync.sh claude]
   context:sync:agents:
     cmds: [bash scripts/context-sync.sh agents]
-  context:sync:cursor:
-    cmds: [bash scripts/context-sync.sh cursor]