security: lefthook + gitleaks secret gate; remove hardcoded credentials

[gHashTag]

Closes #1430

What changed

Same fixes as gHashTag/trinity-fpga PR #900, applied to the files this repo shares with it, plus the secret gate.

• fpga/esp32_wifi_bridge/esp32_wifi_bridge.ino: AP credentials move to a gitignored secrets.h; secrets.h.example added.
• fpga/COMPLETE_CONNECTION_GUIDE.md: placeholders instead of the Wi-Fi password.
• deploy/trinity-nexus/canvas/src/main_gui.zig, src/trinity_node/main_gui.zig: wallet password read from the environment (fails with error.MissingWalletPassword when unset).
• tools/telegram-bridge/2fa-neuro-sage.sh: 2FA password from the environment.
• .gitleaks.toml: shared [extend] + hardcoded-password-literal rule, byte-identical with the canonical copy (gHashTag/t27 PR #6433). Narrow allowlists: synthetic Kaggle data (1381 stripe-pattern false positives), public contract deployment JSON, archived .vibee spec examples, QA fixtures, and three lines (public token address, RFC 6455 example nonce, a registry slot name) plus the S07 prose note.
• lefthook.yml: secret-gate added to the existing pre-commit and pre-push (existing commands kept). This repo uses core.hooksPath=.githooks, whose tracked hooks call lefthook run, so the gate runs without lefthook install.
• .github/workflows/secret-scan.yml: new CI twin scanning the PR / push range.
• .gitignore: secrets.h, .creds. README.md: "Secrets never enter the repository" section (no SECURITY.md here).

The docs/book generators, Kaggle scripts and ralph report script that held keys in trinity-fpga were already reading from the environment here.

Branch is fix/secret-gate, not security/...: the repo's pre-push branch-name rule only accepts feat|fix|docs|refactor|test|chore.

Verified

• gitleaks dir . --config .gitleaks.toml -> exit 0
• staged probe const char* wifi_password = "hunter2hunter2"; -> gitleaks git --staged exit 1 (probe removed)
• lefthook install -> exit 1 (refuses because core.hooksPath is set to .githooks; left as is). The commit went through pre-commit secret-gate and the push through pre-push secret-gate via .githooks.

Credentials to rotate

They were pushed, so removing them does not unpublish them:

• Wi-Fi AP password (ESP32 bridge firmware) - fpga/esp32_wifi_bridge/esp32_wifi_bridge.ino, fpga/COMPLETE_CONNECTION_GUIDE.md
• Wallet password (node GUI) - deploy/trinity-nexus/canvas/src/main_gui.zig, src/trinity_node/main_gui.zig
• Telegram account 2FA password - tools/telegram-bridge/2fa-neuro-sage.sh
• Also in history (already removed from this tree earlier): DeepSeek API key (docs/book generators), Kaggle API token (targets/kaggle scripts), Telegram bot token (.trinity/ralph) - in this repo's git history (added, later removed); rotate them along with the trinity-fpga PR feat(queen): a round has a resolution moment #900 list.

🤖 Generated with Claude Code

[gitguardian]

⚠️ GitGuardian has uncovered 1 secret following the scan of your pull request.

Please consider investigating the findings and remediating the incidents. Failure to do so may lead to compromising the associated services or software components.

🔎 Detected hardcoded secret in your pull request

GitGuardian id	GitGuardian status	Secret	Commit	Filename
37883008	Triggered	Generic Password	0b74c39	tools/telegram-bridge/2fa-neuro-sage.sh	View secret

🛠 Guidelines to remediate hardcoded secrets

1. Understand the implications of revoking this secret by investigating where it is used in your code.
2. Replace and store your secret safely. Learn here the best practices.
3. Revoke and rotate this secret.
4. If possible, rewrite git history. Rewriting git history is not a trivial act. You might completely break other contributing developers' workflow and you risk accidentally deleting legitimate data.

To avoid such incidents in the future consider

• following these best practices for managing and storing secrets including API keys and other credentials
• install secret detection on pre-commit to catch secret before it leaves your machine and ease remediation.

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^{🦉 GitGuardian detects secrets in your source code to help developers and security teams secure the modern development process. You are seeing this because you or someone else with access to this repository has authorized GitGuardian to scan your pull request.}

[github-actions]

X Brain Health Check

Score: 100.0/100
Status: 🟢 HEALTHY
Threshold: 80/100

X Brain is above merge threshold

[github-actions]

🧪 Brain Stress Test Results

Tests: 261/261 passed, 0 leaked
Status: 🟢 PASS
Gate: every test in zig build test-brain-stress passes and none leaks