ABI: broadcast hot-reload readiness to every inspector connection

[chrisbbreuer]

Parent: #140
Profiles: #163, #164
Roadmap: #134
Inspector foundation: #139

Implement the shared pinned BunDebugger__willHotReload boundary as a real process-wide inspector broadcast.

Acceptance:

• Export the exact no-argument C ABI for both pinned Home and Bun profiles.
• Deliver exactly {"method":"Bun.canReload"} to every live inspector connection across all context groups/VMs.
• Do nothing when no inspector connection exists.
• Make broadcast iteration safe when a frontend callback releases itself, releases another session, or reenters the broadcast.
• Never deliver to detached/release-requested sessions, and preserve deterministic per-state session order.
• Add direct, multi-session, multi-VM, detach/reentrancy, and no-session tests with zero leaks.
• Add compiled Home/Bun consumer evidence in Debug and ReleaseSafe.
• Refresh both exact inventories, ABI: define and implement versioned Bun and Home private-JSC profiles #140/ABI: implement the pinned Home private-JSC profile #163/ABI: implement the pinned Bun private-JSC profile #164, and concise ABI documentation.

Backward compatibility is intentionally out of scope; implement the clean exact pinned behavior.

Completion evidence:

• Implementation and exact unit coverage: 1d26c6cc
• Inventories and concise documentation: 6427d1ca
• Focused hot-reload unit slice: 3/3, zero failures/leaks
• Existing inspector detach regression: 3/3, zero failures/leaks
• Exact Home and Bun consumer fixtures: Debug and ReleaseSafe
• Inventories: Home 409/471 (62 pending), Bun 401/461 (60 pending), zero unclassified
• CI gate: test-private-hot-reload is part of private-abi-boundary

[chrisbbreuer]

Completed on main in 1d26c6c and 6427d1c with exact multi-VM, detach/reentrancy, Debug, ReleaseSafe, inventory, documentation, and CI-gate evidence.