docs(roadmap): add #336 — session subcommand resume inconsistency and type/kind error mismatch

[code-yeongyu]

Pinpoint #329

Gap 1: /session vs /session list inconsistent resume-mode support.
Gap 2: Error JSON uses "type" instead of "kind" — breaks generic kind-dispatchers.

Live on b90875f:

claw --output-format json --resume latest /session
→ {"command":"/session","error":"unsupported resumed slash command","type":"error"}
                                                                         ^^^^^ not "kind"

claw --output-format json --resume latest /session list
→ valid session list JSON ✅

Two subcommands of same slash command, different resume contracts, no per-subcommand resume flag in /help JSON.

Fix shape: add resume_subcommands per-command in /help JSON; use kind=error in error responses; regression tests.

ROADMAP.md only