feat(cli): add verbose diagnostics mode

[michiosw]

Summary

• Adds kontext start --verbose and KONTEXT_DEBUG=1 as equivalent opt-in diagnostics modes.
• Adds shared diagnostic helpers with redaction before any raw details reach stderr.
• Keeps default output focused on human summaries.

Why

Normal runs should be quiet, but debugging still needs enough detail to be useful. This gives developers one explicit verbose path and keeps tokens, auth codes, headers, cookies, and OAuth URLs out of terminal output.

Before / After Terminal Capture

Before, raw details had no common redaction/output path:

⚠ Could not create hosted connect session (connect session request failed: 502 Bad Gateway: ...)

After, normal output stays concise and diagnostics are opt-in:

⚠ Could not create hosted connect session.

With --verbose or KONTEXT_DEBUG=1, sensitive values are redacted:

hosted connect session error: token exchange failed: Authorization: Bearer [REDACTED] code=[REDACTED]

Verification

• Ran go test ./... on this branch.

[michiosw]

• feat(hooks): quiet default allow reasons #71
• fix(start): summarize missing provider setup #70
• fix(auth): reject gateway reauth account mismatch #69
• feat(cli): add verbose diagnostics mode #68 👈 (View in Graphite)
• fix(start): preflight agent launch setup #67
• fix(auth): use stable session identity #66
• main

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[michiosw]

Merge activity

• Apr 18, 12:43 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• Apr 18, 12:47 PM UTC: Graphite rebased this pull request as part of a merge.
• Apr 18, 12:49 PM UTC: @michiosw merged this pull request with Graphite.

The base branch was changed.