Adds the complete asset-extension and conversion-action management
surface that AdLoop was missing. Three logical chunks bundled here
because they share `ads/write.py`'s dispatch + apply infrastructure
and would conflict if split into separate PRs.

- `draft_call_asset` — campaign or customer scope, E.164 normalization,
  ad-schedule restriction, optional conversion-action override
- `draft_location_asset` — Google Business Profile-backed AssetSet
  (LOCATION_SYNC), with label/listing filters
- `draft_image_assets` — campaign image extensions from local files
  with MIME + dimension validation
- `draft_callouts`, `draft_structured_snippets`, `draft_sitelinks` —
  refactored to support BOTH campaign-scope AND customer-scope (the
  account-level CustomerAsset path that propagates to every eligible
  campaign automatically)
- `add_ad_schedule` — Mon-Sat 8am-9pm-style scheduling via
  AdScheduleInfo CampaignCriterion
- `add_geo_exclusions` — negative geo CampaignCriterion records to
  shrink a broad include list
- `_apply_assets()` shared helper routing a populate fn through either
  CampaignAsset or CustomerAsset linkage based on scope
- Phone-number E.164 normalization with US/CA + EU trunk-prefix handling

- Update existing RSAs without delete-then-recreate
- Partial update via FieldMask — only the fields the caller passes
  are modified
- Headlines/descriptions accept either bare strings (unpinned) or
  {"text": "...", "pinned_field": "HEADLINE_1"} dicts (pinned)

- `draft_create_conversion_action` — AD_CALL / WEBSITE_CALL / WEBPAGE
  / GA4_CUSTOM with value, threshold, attribution model, counting type
- `draft_update_conversion_action` — partial update with FieldMask;
  rename / promote-demote / set value / change duration threshold
- `draft_remove_conversion_action` — irreversible removal (warns that
  SMART_CAMPAIGN_* and GOOGLE_HOSTED types reject mutation)

The 3 conversion-action tools live in their own module
`adloop/ads/conversion_actions.py` and route through dispatch via
`_apply_*_conversion_action_route` shims kept in `ads/write.py`.

- `link_asset_to_customer` — promote existing Asset rows from
  campaign-scope to account-level (CustomerAsset)
- `update_call_asset` / `update_sitelink` / `update_callout` —
  in-place asset updates with FieldMask
- `draft_promotion` / `update_promotion` — PromotionAsset create
  + swap (PromotionAsset is immutable; update is implemented as
  create-new-link-old-unlink)
- Promotion module uses `enum_names("PromotionExtensionOccasionEnum")`
  + `enum_names("PromotionExtensionDiscountModifierEnum")` from
  the dynamic-enums helper
- Conversion-actions module uses `enum_names("...")` for all 4
  Google Ads enums it validates against — drops 4 hardcoded enum
  sets that were drifting from the SDK
- Auto-cleanup script `scripts/cleanup_sitelink_links.py` for
  duplicate sitelink CampaignAsset detection

- `tests/test_ads_extensions.py` — comprehensive validation +
  apply-handler tests for every new function (uses fake services
  mirroring the google-ads SDK protos; no network)
- `tests/test_conversion_actions.py` — 29 tests
- `tests/test_update_rsa.py` — RSA update integration tests
- All 430 tests pass

…es on create

Two issues surfaced when creating ConversionActions via the Google Ads
API that were not covered by validation:

1. include_in_conversions_metric is IMMUTABLE on create — Google derives
   it from the conversion category and rejects any value supplied in the
   create mutate with IMMUTABLE_FIELD. The apply function previously
   set it unconditionally, blocking every AD_CALL / PHONE_CALL_LEAD
   create with the default True value. Removed the line; callers who
   need to change it use draft_update_conversion_action after create.

2. default_value > 0 paired with always_use_default_value=False is
   rejected as INVALID_VALUE — it reads as "you set a value but told me
   not to use it". The draft tool defaults always_use_default_value to
   False, so the typical "set a default $250 lead value" call kept
   failing with no useful error. Added an auto-correct in the draft
   function: when default_value > 0 and the caller didn't explicitly
   opt out, flip always_use_default_value to True.

Tests added cover both regressions plus a sanity test that callers
who already set the flag correctly still get their value through, and
that default_value=0 keeps the flag False (for snippet-value callers).

All 227 tests pass.