Report ssh_tunnel_event booleans explicitly in telemetry

[anton-107]

Changes

Drop omitempty from all five bool fields on SshTunnelEvent
(libs/telemetry/protos/ssh_tunnel.go): IsSuccess, IsReconnect,
AutoStartCluster, HasBaseEnvironment, HasUsagePolicy.

Why

omitempty drops the zero value, so a failed ssh connect sent no is_success
field at all and landed in the telemetry table as NULL rather than false.
Filtering on is_success = false returned zero rows across all history — any
straightforward "are users hitting errors?" query reported a clean bill of health
while the real IDE-mode failure rate was 40-55%.

All five bools are populated unconditionally in buildSshTunnelEvent, so each
has a meaningful false. The other four were equally unrepresentable and matter
for funnel analysis, so they are fixed in the same pass rather than left to be
rediscovered. ServerStartTimeMs in the same struct already omitted the tag,
which is what confirmed this was a field-level mistake rather than an intended
encoding.

Historical rows cannot be backfilled, so the struct doc comment records the
cutover: queries spanning it must count NULL as failure for pre-fix data.

No changelog fragment — experimental/ changes don't get one until the feature
graduates, and the payload isn't user-visible.

Tests

• New libs/telemetry/protos/ssh_tunnel_test.go: pins the zero-value wire
  payload, plus a reflection guard that fails if a future bool on this struct
  arrives with omitempty.
• New TestBuildSshTunnelEventReportsFailure covers the failure path in
  experimental/ssh/internal/client; the existing table test only ever passed
  true.
• Both new tests were confirmed to fail against the pre-fix tag, with
  actual: <nil> — the exact NULL this fixes.
• Verified end-to-end on the full FrontendLog envelope as uploaded to
  /telemetry-ext: "is_success": false is now transmitted.
• task lint-go (0 issues, all 3 modules), task test-exp-ssh, telemetry and
  ssh acceptance tests pass. One pre-existing failure in
  bundle/templates/lakeflow-integrations, unrelated: it fails identically on
  unmodified origin/main (blocked PyPI fetch in my sandbox).

This PR was written by Claude Code.

[github-actions]

Approval status: pending

/libs/telemetry/ - needs approval

Files: libs/telemetry/protos/ssh_tunnel.go, libs/telemetry/protos/ssh_tunnel_test.go
Suggested: @parthban-db
Also eligible: @simonfaltum, @renaudhartert-db, @hectorcast-db, @tanmay-db, @Divyansh-db, @tejaskochar-db, @mihaimitrea-db, @chrisst, @rauchy

General files (require maintainer)

Files: experimental/ssh/internal/client/client_internal_test.go
Based on git history:

• @rclarey -- recent work in libs/telemetry/protos/, experimental/ssh/internal/client/

_{Any maintainer (@andrewnester, @denik, @pietern, @shreyas-goenka, @simonfaltum, @renaudhartert-db, @janniklasrose, @lennartkats-db, @rugpanov, @rclarey) can approve all areas.
See OWNERS for ownership rules.}

[eng-dev-ecosystem-bot]

Integration test report

Commit: 2dc338b

Run: 32479759911

	Env	💚​RECOVERED	🙈​SKIP	✅​pass	🙈​skip	Time
💚​	aws linux	1	4	274	1162	5:24
💚​	aws windows	1	4	276	1160	3:17
💚​	azure linux	1	4	273	1162	5:14
💚​	azure windows	1	4	275	1160	3:40
💚​	gcp linux	1	4	274	1162	5:45
💚​	gcp windows	1	4	276	1160	3:20

	Test Name	aws linux	aws windows	azure linux	azure windows	gcp linux	gcp windows
💚​	TestAccept	💚​R	💚​R	💚​R	💚​R	💚​R	💚​R
🙈​	TestAccept/bundle/invariant/no_drift	🙈​S	🙈​S	🙈​S	🙈​S	🙈​S	🙈​S
🙈​	TestAccept/bundle/resources/vector_search_endpoints/drift/recreated_same_name	🙈​S	🙈​S	🙈​S	🙈​S	🙈​S	🙈​S
🙈​	TestAccept/bundle/resources/vector_search_indexes/recreate/embedding_dimension	🙈​S	🙈​S	🙈​S	🙈​S	🙈​S	🙈​S
🙈​	TestAccept/ssh/connection	🙈​S	🙈​S	🙈​S	🙈​S	🙈​S	🙈​S

Top 6 slowest tests (at least 2 minutes):

duration	env	testname
3:57	azure linux	TestAccept
3:51	gcp linux	TestAccept
3:49	aws linux	TestAccept
3:35	azure windows	TestAccept
3:13	aws windows	TestAccept
3:02	gcp windows	TestAccept