feat(api): strict workspace isolation + agent parity fixes

Enforce workspace isolation at every layer:

- Router: move RequireWorkspaceMember middleware to group level so ALL
  workspace-scoped routes (issues, agents, skills, runtimes, inbox,
  comments) require workspace context
- SQL: add GetXxxInWorkspace queries that filter by workspace_id,
  eliminating cross-workspace data access at the query level
- Handlers: loadXForUser functions use workspace-scoped queries,
  no fallback to unscoped queries
- Migration 025: add workspace_id column to comment table with backfill
- ListComments: add workspace_id filter for defense-in-depth

Fix daemon workspace mapping:
- Server returns workspace_id in task claim response (from issue)
- Daemon uses task.WorkspaceID directly instead of unreliable
  workspaceIDForRuntime() local map lookup
- Remove workspaceIDForRuntime function

Fix agent/human parity:
- Comment update/delete: use resolveActor for isAuthor check so agents
  can edit/delete their own comments
- Event attribution: replace hardcoded "member" with resolveActor in
  agent, skill, and subscriber publish calls

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/pkg/db/queries/agent.sql

@@ -7,6 +7,10 @@ ORDER BY created_at ASC;
 SELECT * FROM agent
 WHERE id = $1;
 
+-- name: GetAgentInWorkspace :one
+SELECT * FROM agent
+WHERE id = $1 AND workspace_id = $2;
+
 -- name: CreateAgent :one
 INSERT INTO agent (
     workspace_id, name, description, avatar_url, runtime_mode,