[roll] Roll fuchsia [beads] Improve migrating-host-tool-to-bazel skill and trim noise

Improves the `migrating-host-tool-to-bazel` skill with gotchas and
practices learned during migration, and trims unnecessary context:

- Trims the generic "Persona" section to save context space.
- Compresses Step 1 (Create Bazel targets) instructions.
- Replaces the slow and potentially disruptive `fx set` commands
  with `fx gen` for intermediate GN validation.
- Explains when to use `fx set` (only to configure tests if needed).
- Fixes the `verify_bazel2gn` target registration path to use
  `build/bazel2gn_verification_targets.gni` instead of `build/BUILD.gn`.
- Adds a gotcha for missing test-only dependencies when moving test
  sources from `go_library` to `go_test` in GN.
- Adds a gotcha for `fx add-host-test` when testing host-only tests.

Test: None, documentation update.

TAG=agy
CONV=f2307339-1329-4a48-bcdf-c5ae19894e14

Original-Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1623394
Original-Original-Revision: bf94ec779ca3c5f3bf51dab20afe579fb29844d5
GitOrigin-RevId: 6588ad552a29cb12a9b3a6918fbf674a8960f883
Change-Id: Ib839875d337181541cb9ec74856337d2efacad8e
Reviewed-on: https://fuchsia-review.googlesource.com/c/integration/+/1622165
Cr-Commit-Position: refs/heads/main@{#193322}