Add OpenTelemetry infrastructure for distributed tracing with support
for W3C Trace Context propagation from CI systems.

- Add telemetry package with tracer initialization, shutdown, and trace context parsing
- Implement OTelReporter with build and package span creation
- Add CLI flags: --otel-endpoint, --trace-parent, --trace-state
- Capture build metrics, package timing, and GitHub Actions context
- Thread-safe concurrent package builds with RWMutex
- Graceful degradation when tracing fails
- Comprehensive tests with in-memory exporters
- Documentation in docs/observability.md and README.md

Closes CLC-2106

Co-authored-by: Ona <no-reply@ona.com>

Enable Docker support in the development container for building and
testing Docker packages.

Co-authored-by: Ona <no-reply@ona.com>

Move tracer shutdown from getBuildOpts to build command Run function
to ensure spans are flushed after the build completes, not immediately
after getBuildOpts returns.

- Change getBuildOpts to return shutdown function
- Update all callers to handle the new return value
- Set OTEL_EXPORTER_OTLP_ENDPOINT from CLI flag before InitTracer

Tested with Jaeger and confirmed traces are now properly sent.

Co-authored-by: Ona <no-reply@ona.com>

- Fix errcheck warnings in test files (check tp.Shutdown errors)
- Fix errcheck warnings for os.Setenv/Unsetenv in tests
- Run go fmt on modified files

Co-authored-by: Ona <no-reply@ona.com>

Format all Go files to ensure consistent code style.

Co-authored-by: Ona <no-reply@ona.com>

Add comprehensive tests for GitHub Actions environment variable handling:
- TestOTelReporter_GitHubAttributes: Verifies all 10 GitHub attributes
  are correctly added to spans when running in GitHub Actions
- TestOTelReporter_NoGitHubAttributes: Verifies no GitHub attributes
  are added when not running in GitHub Actions

Coverage improvement:
- addGitHubAttributes: 9.1% → 100%

Co-authored-by: Ona <no-reply@ona.com>

Change InitTracer to accept endpoint as parameter instead of reading
from environment variable. This improves testability and follows
separation of concerns.

Changes:
- InitTracer now takes endpoint as parameter: InitTracer(ctx, endpoint)
- Remove confusing env var manipulation in cmd/build.go
- Simplify test (no need to manipulate environment)
- Make configuration flow clearer: flag → function parameter

Benefits:
- Easier to test (no env var side effects)
- Clearer API (explicit parameter vs implicit env var)
- Consistent with other reporters (e.g., SegmentReporter)
- No circular dependency between flag default and env var

Co-authored-by: Ona <no-reply@ona.com>

- Add OTEL_EXPORTER_OTLP_INSECURE env var and --otel-insecure flag
- Default to secure TLS connections (production-ready)
- Fix version retrieval to use actual leeway.Version
- Update documentation with Honeycomb production examples
- Add TLS configuration section to observability docs

Addresses review feedback on PR #288

Co-authored-by: Ona <no-reply@ona.com>