Reduce Sentry noise: demote non-actionable report_error! calls in MCP + credentials

[warp-dev-github-integration]

Description

Audits every report_error! call in the AI MCP and cloud-credential code paths and demotes the ones that don't represent actionable engineering issues from Sentry events to log::warn! breadcrumbs, to reduce Sentry noise. Guided by .agents/skills/logging-and-error-reporting/SKILL.md (a non-actionable failure is one an engineer can't act on: network/transient failures, expected fallbacks, and gracefully-handled conditions). Demoting to Warn mirrors what report_error! itself already does at runtime for non-actionable errors (logged at Warn, never sent to Sentry).

Demoted to log::warn! (12):

• app/src/ai/aws_credentials.rs — STS AssumeRoleWithWebIdentity SDK error (network/transient; also a non-sink duplicate of the load-credentials sink) and the credential-load sink (surfaced to the user via the Failed state).
• app/src/ai/bedrock_credentials.rs — STS error in the background refresh loop, which already retries with backoff.
• app/src/ai/geap_credentials.rs — credential mint failure that is explicitly, gracefully handled (keeps the previous token or surfaces a Failed state).
• crates/mcp/src/oauth.rs — secure-storage (keychain) write failure — environmental/recoverable; the read path already treats these as warn.
• crates/mcp/src/runtime.rs — MCP child-process stderr read failure (expected terminal condition when the child exits).
• app/src/ai/mcp/templatable_manager/native.rs — three model_event_sender.send failures (receiver dropped during shutdown = teardown race), a benign installed-server lookup miss in update dedup, and per-server legacy→templatable conversion failures at startup (e.g. template already exists).
• app/src/ai/mcp/mod.rs — reading MCP env vars from sqlite, which expectedly misses (falls back to config defaults).

Kept as report_error! (9): genuine invariant violations that warrant a Sentry issue — serialization of our own types "that should never fail" (mod.rs ×2, templatable_installation.rs, oauth.rs), internal-consistency checks (missing installation/template mappings, template with no servers), and resolved-config JSON parse failures in native.rs.

Unused report_error imports were removed from the four files where every call was demoted.

Note for the reviewer: the mod.rs sqlite env-var read is the most debatable demotion — the logging skill's canonical example reports sqlite read failures, but here the lookup expectedly misses and gracefully falls back to defaults. Happy to keep it as report_error! if you'd prefer.

Linked Issue

N/A — requested via the factory-client bug-triage Slack thread (linked below).

Testing

No behavior changes — only the log level / Sentry-reporting of these call sites changed, so no new automated test was added.

• ./script/format passes.
• cargo clippy -p warp -p mcp --all-targets --tests -- -D warnings passes (the affected crates; CARGO_BUILD_JOBS=1).

Agent Mode

• Warp Agent Mode - This PR was created via Warp's AI Agent Mode

CHANGELOG-NONE