BJ-0: Add 'jira' to platform unions + audit 'github' hardcodes#

Summary#

Add 'jira' to the two platform union types and verify — via grep — that no platform === 'github' equality branches exist in src/dispatch/, src/phase-router/, src/tenant/, or src/invoke/. This unblocks Wave 1 of the Atlassian integration epic.

Files#

Steps#

1. Extend the platform union in dispatch-event.dto.ts:19 and dispatch-event.dto.ts:37 to 'github' | 'bitbucket' | 'gitlab' | 'jira'.
2. Extend the platform union in tenant-config.interface.ts:9 to 'github' | 'gitlab' | 'bitbucket' | 'jira'.
3. Run npx tsc --noEmit and confirm zero errors.
4. Run npm run test and confirm all unit tests pass unchanged.
5. Capture grep report (commands + output) proving no platform === 'github' equality checks exist in the four audited paths — include verbatim in PR body.

Verification#

• npx tsc --noEmit → 0 errors after the union changes.
• npm run test → all suites green, no snapshot drift.
• PR body contains the grep transcript for all four paths showing no matches.

Risks#

• Target branch is rc/atlassian-integration per the issue; current worktree sits on rc/multi-tenant. Delivery agent must rebase/target the correct branch before opening the PR.

Assumptions#

• The pre-existing 'github' literals in tenant-config.service.ts:20 (default config value) and tenant.module.ts:10 (default provider name) are configuration values, not equality branches, so they are out of scope for the audit.