feat(tui): configure every notification provider inside Settings

[Yeachan-Heo]

Problem

Settings → Notifications currently exposes notification providers unevenly: Telegram can be configured in the TUI, while Discord and Slack are effectively non-configurable from the settings UI. Users must leave the TUI and manipulate configuration through another surface.

Required UX contract

Make every supported notification adapter configurable end-to-end inside the TUI settings flow, including Discord and Slack.

At minimum:

• list every supported notification provider in Settings → Notifications;
• provide provider-specific setup/edit screens for all required fields;
• show safe masked/fingerprinted secret state without echoing full tokens/webhooks;
• support enable/disable, edit, validation/test delivery, and recovery from invalid/incomplete configuration;
• explain missing prerequisites and actionable errors in the TUI rather than presenting a dead/non-configurable row;
• preserve the existing config schema, trust boundaries, and redaction rules unless a schema change is strictly required;
• cover keyboard navigation, cancellation/back behavior, persistence/reload, malformed config, and provider-specific validation with deterministic tests;
• update user-facing notification setup documentation.

This supersedes the incomplete UX closure of #2050 / #2088: moving notification setup into settings is not complete while supported Discord and Slack adapters cannot actually be configured there.

Owner directive source: Discord #gajae-code-dev, 2026-07-30 07:55 UTC.

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[repo owner's gaebal-gajae (clawdbot) 🦞]

[Yeachan-Heo]

Owner directive accepted. This is assigned to the existing TUI/input subsystem batch for deep-interview, implementation, focused settings/config/adapter tests, and a dev PR. The active owner must preserve token/webhook redaction and provide in-TUI validation/test delivery for every supported adapter.

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[repo owner's gaebal-gajae (clawdbot) 🦞]

[Yeachan-Heo]

Resolved on dev (HEAD b014ec1da) by merged PR #3622 (commit 0cc1536db0705154c5f0454e0b62694f29427a7a): add first-class notification provider settings

Verified the fix is an ancestor of the current dev HEAD. Closing as resolved.