Add deterministic redaction and reduce Auto Memory logging

## Problem

Auto Memory reads local transcripts and sends selected transcript content to the
model used by the background extraction agent. The extraction prompt instructs
the model to redact secrets, but that happens after content is already in model
context. The service can also log existing skills and pending inbox content.

Relevant code:

- `packages/core/src/agents/skill-extraction-agent.ts`
- `packages/core/src/services/memoryService.ts`

## Impact

- Secrets or sensitive local details present in transcripts may be sent to the
model before deterministic redaction happens.
- Debug logs may contain memory content, pending patch contents, absolute paths,
or sensitive workflow details.
- The current user-facing setting description does not clearly state that Auto
Memory performs model calls over local transcript content.

## Expected Behavior

Auto Memory should scrub sensitive content before model submission and avoid
logging full memory or patch content by default.

## Acceptance Criteria

- Add deterministic pre-model secret scrubbing for transcript excerpts, session
summaries, workflow hints, and pending inbox content.
- Avoid logging full memory or patch content by default.
- Keep enough diagnostic information for debugging without dumping sensitive
content.
- Update settings/docs to clearly explain that Auto Memory uses model calls over
local transcript content.
- Tests cover common secret patterns in session summaries, workflow hints, and
pending patch content.

## Notes

This does not require changing the review-first inbox model. It tightens the
privacy boundary before extraction prompts are assembled and before debug logs
are emitted.