fix(api): clean dynamic API HTTP and connection errors

[arseniy-pplx]

Summary

Dynamic tangle api <group> <op> calls (and the OpenAPI schema refresh/fetch path) now fail with a concise, one-line, credential-safe message and a non-zero exit code instead of a raw traceback or a truncated HTTP status exit code.

• HTTP status errors render as HTTP <status> <reason> for <METHOD> <url> with a whitespace-normalized, length-bounded slice of the backend body.
• Connection, timeout, proxy, and TLS errors render an actionable reason (e.g. connection failed: [Errno 111] Connection refused, read timed out, TLS error: ...).
• URL sanitization strips user:pass@ userinfo and redacts credential query params, Authorization, and presigned/SAS-URL signatures (AWS SigV4 / GCS / Azure). IPv6 literals are re-bracketed so host and port survive redaction (https://<redacted>@[2001:db8::1]:8443/...).
• Free-form exception text is scrubbed for embedded URLs and bare user:pass@host userinfo before display, so a crafted or third-party proxy/connect error string cannot leak credentials — while benign diagnostics (errno, TLS reason) are preserved.
• Exit codes are a non-zero string exit (1) rather than the raw HTTP status, which was previously truncated to 8 bits (404 → 148, 512 → 0 false success).
• Schema refresh/fetch failures reuse the same formatting and keep omitting the /openapi.json response body, so an auth failure cannot reflect the credentials just sent.

The original exception is preserved as the cause (raise ... from exc) for Python callers; programmatic clients still receive raw httpx exceptions. Changes are confined to api_transport.py and api_cli.py; the existing actionable cache-missing behavior and API command exit semantics are unchanged.

Context

Dynamic tangle api calls previously surfaced backend failures either as a raw traceback or as an HTTP status pushed through the process exit code, where the value was truncated to 8 bits (404 → 148, 512 → 0 false success). This renders every failure as one concise, credential-safe line with a correct non-zero exit code, without changing the success path or the actionable cache-missing behavior.

Testing

• uv run pytest tests/test_api_transport.py — URL sanitization (userinfo, credential/query params, presigned signatures, IPv6 re-bracketing with userinfo+port), one-line status errors, bounded/normalized detail, detail omission, actionable request-error classification, embedded-secret scrubbing for proxy/connect exception text, and benign errno/TLS diagnostics preserved
• uv run pytest tests/test_api_cli.py — passes except one pre-existing failure (test_official_static_command_without_schema_fails_with_actionable_error) that reproduces identically on the base commit and is unrelated to this change
• uvx ruff check on the touched files
• uv lock --check; uv build
• git diff --check
• dynamic CLI smoke against a refused port with URL credentials renders Failed to reach GET http://<redacted>@127.0.0.1:1/api/pipeline_runs/: connection failed: [Errno 111] Connection refused, exit 1