## Summary

- Fixes silent telemetry loss on SPOG (custom-URL) hosts when connecting
to an all-purpose cluster via an httpPath like
`sql/protocolv1/o/<workspace-id>/<cluster-id>`.
- `extractSpogHeaders` now extracts the workspace ID from the
`/o/<wsid>/` path segment as a fallback when `?o=<wsid>` is not present,
and emits an `x-databricks-org-id` header so the wrapped
`telemetryClient` / feature-flag client can route correctly on SPOG.
- Priority order preserved: `?o=` in `httpPath` ▶
`/sql/protocolv1/o/<wsid>/` path segment. Caller-set request headers
still win, including mixed-case `X-Databricks-Org-Id`.

## Why

On a SPOG host the workspace identity has to be in either the URL or the
`x-databricks-org-id` header for PoPP to route a request to the correct
workspace. For all-purpose cluster Thrift this is free — the workspace
ID is in the `/o/<wsid>/` segment of httpPath, so PoPP routes Thrift via
`routing_reason=workspace-id` and the session opens fine without an
explicit `?o=`.

The telemetry and feature-flag transports built by `connector.Connect`
wrap `c.client` with `withSpogHeaders` only when
`extractSpogHeaders(c.cfg.HTTPPath)` returns a non-nil map. Before this
PR that only happened when `?o=` was present, so cluster URLs without
`?o=` produced no `x-databricks-org-id` header, PoPP fell back to
default (account) routing on `/telemetry-ext`, and the responses were
303 redirects to `/login` — silently dropping telemetry on SPOG.

## What changes

`connector.go`
- New `clusterPathOrgIDPattern` regex
(`(?:^|/)sql/protocolv1/o/(\d+)/[^/?]+`) compiled once at package init.
- `extractSpogHeaders` checks `?o=` first (existing behavior), then
falls back to the cluster path segment, then returns nil. The
malformed-query-string path now also falls through to path inspection
instead of returning early. Log messages indicate which source produced
the workspace ID.
- Updated the connection comment to describe both query-param and
cluster-path extraction.
- `regexp` added to imports.

`connector_spog_test.go`
- Four new table entries under `TestExtractSpogHeaders`:
  - Cluster path without `?o=` → header extracted from `/o/<wsid>/`
  - Cluster path with leading `/` → same
  - Cluster path with `?o=` → query-param value wins
- Warehouse path without `?o=` → still nil (regression guard: the new
regex must not match warehouse paths)
- New transport regression test proving a mixed-case caller-set
`X-Databricks-Org-Id` is not overwritten by the SPOG wrapper.

## Test plan

- [x] `go test -run
'TestExtractSpogHeaders|TestHeaderInjectingTransport' -v .` — focused
SPOG extraction and transport tests pass.
- [x] `go test -short .` — root package suite passes.
- [x] Behavior validated on the OSS JDBC equivalent fix against Prod
SPOG (`peco.azuredatabricks.net`) all-purpose cluster: telemetry POST
`/telemetry-ext` flipped from `HTTP 303 → /login` to `HTTP 200 OK` once
the path-segment extraction populated `x-databricks-org-id`. Same shape
of fix here.

## Out of scope

- The corresponding OSS JDBC driver fix is opened as
databricks/databricks-jdbc#1475.
- The Python connector (`databricks/databricks-sql-python`) has a
sibling upstream-head PR for the same fix:
databricks/databricks-sql-python#817.
- The Node.js connector (`databricks/databricks-sql-nodejs`) already
extracts org ID from both query param and path segment (see
`extractWorkspaceId` in `lib/DBSQLClient.ts`).

This pull request and its description were written with assistance from
Claude Code.

---------

Signed-off-by: Madhavendra Rathore <madhavendra.rathore@databricks.com>