docs(readme): reorganize docs and screenshot gallery

Align project docs with current behavior using progressive disclosure and bilingual deep-dive guides. Add per-page admin screenshots with consistent page-* naming to make UI documentation clearer.

docs/review-engines.md

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+# Review Engines
+
+## Overview
+
+The system supports two engines:
+
+- `agent`: native staged review pipeline
+- `codex`: Codex CLI-backed review pipeline
+
+Engine is selected by `REVIEW_ENGINE` runtime configuration.
+
+## Agent engine
+
+Agent engine classifies changes and dispatches specialist tasks.
+
+### Review modes
+
+- `skip`: low-risk changes may bypass specialist review
+- `light`: minimal specialist checks for low-risk code changes
+- `full`: full specialist review for risky or larger changes
+
+### Size policy
+
+`small`/`medium`/`large` thresholds are used by triage to choose mode and token budgets.
+
+## Codex engine
+
+Codex engine runs review through Codex CLI with independent runtime settings:
+
+- `CODEX_API_URL`
+- `CODEX_API_KEY`
+- `CODEX_MODEL`
+- `CODEX_TIMEOUT_MS`
+- `CODEX_REVIEW_PROMPT`
+
+## Event support
+
+Both engines process:
+
+- Pull request webhook events
+- Commit status webhook events
+
+## Output
+
+- PR/commit summary comment
+- Line-level findings with confidence and severity