fix: add --broadcast to forge create examples and fix broken links

[erhnysr]

What

Four small, verified doc fixes in build-on-base:

1. forge create won't deploy without --broadcast — references/deploy-contracts.md
   Since Foundry v1.0, forge create only simulates unless --broadcast is passed. The testnet and mainnet examples were missing it, so following them verbatim on a current Foundry prints a successful-looking result but never sends the deploy transaction. Added --broadcast to both commands.

2. Broken NOTIFICATIONS.md links — references/migrations/minikit-to-farcaster/mapping.md
   The useNotification section linked to NOTIFICATIONS.md twice, but no such file exists anywhere in the repo. Replaced both with the Farcaster Mini App notifications guide (https://miniapps.farcaster.xyz/docs/guides/notifications).

3. Link text / URL mismatch — references/deploy-contracts.md
   The API key step's link text said basescan.org/myapikey / etherscan.io/myapikey while the URLs pointed to /apidashboard. Updated the text to match the (current) URLs.

4. Broken wallet-setup link — references/agents/register.md
https://docs.base.org/ai-agents/guides/wallet-setup does not exist as a wallet guide — it resolves to the Base MCP quickstart page, and no wallet-setup page is listed in docs.base.org/llms.txt. Since the step is for a user who has no wallet, pointed them to the Base App (https://base.app) where they can create a Base Account and obtain an address.

Why

Each is an objectively verifiable error a reader would hit directly — a deploy command that silently no-ops, dead links, and a link whose destination doesn't match its promised content. Docs-only, no behavioral/spec changes.

Testing

• Confirmed NOTIFICATIONS.md does not exist in the repo.
• Confirmed no other --broadcast reference existed in the skill.
• Verified via fetch that docs.base.org/ai-agents/guides/wallet-setup serves MCP-connection content (not wallet setup) and that no wallet-setup page is listed in llms.txt; confirmed https://base.app is the live Base Account entry point.

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1

[erhnysr]

All four fixes were verified rather than assumed:

1. forge create --broadcast — confirmed no other --broadcast reference existed anywhere in the skill; the examples would otherwise only simulate on Foundry v1.0+.
2. NOTIFICATIONS.md — confirmed via repo-wide search that no such file exists (the two links were dead).
3. API-key link text/URL — the visible text (/myapikey) did not match the actual href (/apidashboard); updated text to match.
4. wallet-setup link — fetched https://docs.base.org/ai-agents/guides/wallet-setup and confirmed it serves the Base MCP quickstart (not a wallet guide), and that no wallet-setup page is listed in docs.base.org/llms.txt; confirmed https://base.app is the live Base Account entry point (account.base.app 302-redirects there).

Docs-only changes, no behavioral/spec impact.