docs(ri-050): forge fail-closed docs + TASKS status catch-up (#1275)

Rebased onto next post-#1278. README + skills/mosaic-forge/SKILL.md
document the FORGE_NO_EXECUTOR fail-closed rule + --simulate (fast-follow
to RI-2-001, now merged). TASKS.md rows updated to measured state:
RI-0-001/RI-1-001/RI-1-002/RI-2-001 done (merged with reviews+CI evidence);
RI-2-002/RI-3-001/RI-4-001/RI-5-001 in-progress (PRs open, approved,
merge-queued); RI-3-002/RI-V-001 not-started.

skills/mosaic-forge/SKILL.md

@@ -133,10 +133,13 @@ When the full `@mosaicstack/forge` package is available, Forge uses MACP task ex
 
 ```bash
 # Run from CLI
-mosaic forge run path/to/brief.md
+# Fails closed with a typed FORGE_NO_EXECUTOR capability error when no real
+# executor is wired — pass --simulate to opt into explicit typed simulation
+# (every result carries status `simulated`, which satisfies nothing).
+mosaic forge run path/to/brief.md [--simulate]
 
-# Resume interrupted run
-mosaic forge resume .forge/runs/20260401-143022/
+# Resume interrupted run (same fail-closed rule as forge run)
+mosaic forge resume .forge/runs/20260401-143022/ [--simulate]
 
 # Check status
 mosaic forge status .forge/runs/20260401-143022/