Migrate legacy Pairing workflow to Angular

[nllong]

What

Migrates the legacy AngularJS Pairing workflow (pairing_controller/pairing.html,
/data/pairing/:importfile_id/{properties|taxlots}) to this app, per MIGRATION.md's
"Not yet migrated" checklist.

Changes

• New PairingComponent at route data/pairing/:id/:type:
  • Property / Tax Lot tab switcher (seed-page-inventory-tab), cycle selector (defaults to the
    import file's cycle), and a Show All / Show Paired / Show Unpaired filter on the left grid.
  • Two ag-grid grids side by side. Rows are dragged from the left grid and dropped onto a row
    in the right grid to pair them, using ag-grid Community's addRowDropZone /
    getRowDropZoneParams (no Enterprise license needed).
  • Right grid has a "Paired" column (pinned right) rendering chips for each currently-paired
    counterpart, with a per-chip unpair button.
• PairingService.pairInventory added (mirrors the existing unpairInventory), calling the same
  /api/v3/{properties|taxlots}/{id}/pair/ endpoints the legacy app already uses.
• dataset.component.ts's "Data Pairing" action now navigates to the new route instead of
  console.log.
• datasets.routes.ts: added pairing/:id/:type.
• ag-grid-modules.ts: registered the missing RowDragModule (required by the cross-grid drag
  APIs used here; not previously needed by any other page).

Design decision

The legacy app has a separate Pairing Settings page with its own localStorage-persisted
column visibility/order config. Rather than porting that as a second, parallel column-config
mechanism for a single page, this PR reuses the List View Profile column selector already used on
the Properties/Tax Lots list pages (each grid's columns follow the user's currently selected list
profile for that type). MIGRATION.md records this: Pairing workflow moved to "Already
migrated", Pairing settings moved to "Won't migrate" with the rationale above.

Validation

pnpm lint and pnpm build pass.

Additionally did a full manual/live pass: spun up the Django backend locally (docker), seeded a
test org/cycle with paired and unpaired properties/tax lots, and drove the page end-to-end with a
browser (Playwright) — sign-in, tab switching, cycle/show filters, drag-and-drop pairing, and
unpair-by-click. That pass caught and fixed several bugs that lint/build alone couldn't have:

• RowDragModule not registered, so drag-and-drop silently threw and did nothing.
• Paired-chip labels always showed #<id> instead of an address, because the live API suffixes
  field names with a unique column id (e.g. address_line_1_11) that a literal field-name lookup
  didn't account for.
• The "Paired" column, unpinned, could scroll far out of view for orgs with many columns.
• Switching the Property/Tax Lot tab updated the URL and tab highlight but not the actual grids or
  page title, because Angular reuses the same component instance across the sibling
  properties/taxlots routes and the type route param was only read once at construction.

All four are fixed in this PR and re-verified live afterward.

Screenshots

Hosted as release assets (not committed to the repo — safe to delete after this PR merges/closes).

Pairing page overview (Show All, one paired and two unpaired tax lots):

Right after a drag-and-drop pairing action (dragged a property row onto TL-300; new "333 Pine Rd" chip appears, unpair (✕) buttons on each paired chip):

"Show Unpaired" filter narrowing the left grid to only the remaining unpaired property: