Emit E_PROVISION_CONFLICT for uv sync resolution conflicts

[rugpanov]

Why

databricks environments setup-local wrapped every uv sync failure as
E_PROVISION. The VPEX extension's recovery flow needs to distinguish a
dependency version conflict — the project's dependencies can't be satisfied
against the pins this command wrote — from a generic sync failure it can't fix by
relaxing constraints (a build-backend error, a permissions problem, a transport
error, or an unavailable package). Constraints are already written at the point of
failure (merge precedes provision, so error.diskMutated=true), which the recovery
flow relies on. Fixes DECO-28365.

What

• New error code E_PROVISION_CONFLICT (libs/localenv/result.go), emitted
  from the provision phase.
• Classification is gated on the CLI's own conflict detection, not on uv's
  output. The merge phase already detects a provable version conflict between the
  user's dependencies and the environment pins and records it as the
  W_USER_CONSTRAINT_CONFLICT warning (libs/localenv/warnings.go, PEP 440
  interval math on provably-disjoint ranges). When a uv sync failure coincides
  with that warning, the failure is that conflict surfacing, so it is reported as
  E_PROVISION_CONFLICT (libs/localenv/pipeline.go, hasConstraintConflictWarning).
  Every other sync failure keeps E_PROVISION.
• This is deliberately precise, not broad: an unavailable package or a
  requires-python mismatch (neither is a W_USER_CONSTRAINT_CONFLICT) stays
  E_PROVISION, so a consumer never gets a conflict code for a failure that
  relaxing constraints can't fix. It also needs no stderr string-matching.
• The failing phase (provision), diskMutated=true, and the E_CANCELED
  reclassification are unchanged. PostProvision (pip seed) and EnsurePython
  keep their existing codes.
• Telemetry: adds SetupLocalErrorCodeProvisionConflict and the mapping case
  (cmd/environments/telemetry.go, libs/telemetry/protos/setup_local.go), kept
  exhaustive by the linter and TestErrorCodeCoversLocalenv. A matching value in
  the universe lumberjack proto should follow (ingestion ignores unknown values,
  so the two PRs can land in either order).

Testing

• Unit (libs/localenv/pipeline_test.go): a uv sync failure with a
  merge W_USER_CONSTRAINT_CONFLICT → E_PROVISION_CONFLICT
  (failurePhase=provision, diskMutated=true); a uv sync failure without
  it — even one whose stderr looks like a resolver error → E_PROVISION. Both
  cross-platform.
• Acceptance (acceptance/localenv/provision-conflict/): a real setup-local
  run where the user pins pip==24.0 and the remote constraints pin pip<24, so
  the merge flags the conflict; a fake uv on PATH (the psql acceptance
  precedent — a real uv sync conflict needs a specific managed Python installed
  offline, which CI can't guarantee) fails uv sync. The golden asserts
  error.code=E_PROVISION_CONFLICT, failurePhase=provision, diskMutated=true,
  and the W_USER_CONSTRAINT_CONFLICT warning. Windows-disabled like the psql
  tests; the unit tests cover the logic cross-platform.
• gofmt, go vet, golangci-lint (root module), and go build ./... clean.

Stacked on #6464. Review/merge that first; this PR's base will retarget to
main once #6464 lands.

This pull request and its description were written by Isaac.

[github-actions]

Approval status: pending

/acceptance/localenv/ - needs approval

6 files changed
Suggested: @anton-107
Also eligible: @rclarey, @misha-db

/cmd/environments/ - needs approval

Files: cmd/environments/telemetry.go, cmd/environments/telemetry_test.go
Suggested: @anton-107
Also eligible: @rclarey, @misha-db

/libs/localenv/ - needs approval

Files: libs/localenv/pipeline.go, libs/localenv/pipeline_test.go, libs/localenv/result.go
Suggested: @anton-107
Also eligible: @rclarey, @misha-db

/libs/telemetry/ - needs approval

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

General files (require maintainer)

Files: .nextchanges/cli/setup-local-provision-conflict.md
Based on git history:

• @janniklasrose -- recent work in .nextchanges/cli/

_{Any maintainer (@andrewnester, @anton-107, @denik, @pietern, @shreyas-goenka, @simonfaltum, @renaudhartert-db, @janniklasrose, @lennartkats-db, @rclarey) can approve all areas.
See OWNERS for ownership rules.}