Add Jira multi-account support, connection-aware sync/matching, and related fixes

[batoolfatima05]

Implements docs/JIRA_MULTI_ACCOUNT_PLAN.md end to end:

• Task 1-2: JiraConnection + OrgProjectConnection schema and repo/service
  layer (create/list/get/delete/set-default, encrypted tokens, delete
  blocked while referenced, default-switch atomicity).
• Task 3: Flask + Next.js API endpoints for managing connections, proxied
  through the backend so business rules live in one place.
• Task 4: connection-aware sync -- JiraETLHandler loops JiraConnection
  rows (falling back to the legacy Integration row when none exist),
  scoped ticket idempotency keys, fixed get_org_providers so a
  connection-only org actually syncs.
• Task 5: PR<->ticket matching scoped by connection for the rare
  colliding-key case, without changing the default org-wide matching
  behavior for every ordinary org.
• Task 6: connections management UI folded into the existing Jira card
  (not a second card), site-URL normalization (a pasted
  "https://x.atlassian.net/" was being stored verbatim and building an
  unreachable URL at search/sync time), and a connection picker for
  per-team Jira project search/save (jira_project_search.ts,
  team_projects.ts), closing the OrgProjectConnection write-side gap
  from Task 4.

Also, found while verifying against a 15-scenario Jira<->PR<->deployment
spec:

• PR<->ticket matching now scans only the PR title (previously also
  scanned branch name and description) -- the PR title is the sole
  authoritative source per that spec; branch/description/commit are
  never used as a fallback.
• New TeamRepoProjectMapping: an explicit, informational repo<->Jira-
  project pairing per team (never affects matching/sync/metrics).
• Team creation no longer hard-requires a Git repo -- an opt-in
  "Jira-only, no Git repo" checkbox lets an org with only Jira create a
  team, without changing the default repo-required flow for anyone who
  doesn't check it.
• DoraMetricsBody's empty-state check no longer ignores Jira ticket-
  cycle-time data -- a repo-less team with real ticket data was always
  falling into "configure team repos" instead of showing it.
• Fixed a real, live bug: teams/v2.ts's default code-provider list
  omitted Bitbucket in two places, undercounting a team's repos on the
  team list and leaving its edit-form repo picker empty even when a
  Bitbucket repo was genuinely linked and its metrics were computing
  correctly.
• Fixed a frontend bug in the Repo <-> Project pairing UI: the project
  id was read from the wrong API field (org_project_id instead of id),
  which made every project compare equal to every other one in the
  picker -- selecting one project visibly selected a different one.
• Fixed a backend 500 on saving repo/project pairings: TeamRepoProjectMapping's
  composite primary key was being built from a mix of uuid.UUID and plain
  str values across rows, which broke SQLAlchemy 2's insertmanyvalues
  sentinel matching on bulk insert.

Backend: 567 tests passing, flake8/black clean. Frontend: tsc --noEmit
clean; new/touched test files verified individually.

Co-Authored-By: Claude Sonnet 5 noreply@anthropic.com