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.

README.md

@@ -138,9 +138,9 @@ mosaic brain tasks
 mosaic brain conversations
 
 # Agent forge pipeline
-mosaic forge run
+mosaic forge run [--simulate]        # fails closed (FORGE_NO_EXECUTOR) with no executor wired; --simulate for typed simulated runs
 mosaic forge status
-mosaic forge resume
+mosaic forge resume [--simulate]     # same fail-closed rule as forge run
 mosaic forge personas
 
 # Structured logging