docs(skill): add explicit HTTP verb guidance for server actions in agent skill

[vivek7405]

Closes #1367

Add a comprehensive HTTP Verbs Decision Guide for server actions to .agents/skills/webjs/ (SKILL.md, references/data-and-actions.md, references/muscle-memory-gotchas.md) and the website documentation (website/app/docs/server-actions/page.ts).

Summary of Changes

1. Form-Bound Actions: Clarified that form-bound actions (<form action=${fn}>) strictly require POST (default). Binding a GET action to a form produces a 405 runtime error and webjs check violation (form-action-not-a-get-action). Manually setting method="get" on a bound form emits a WEBJS_FORM_SUBMITTED_AS_GET diagnostic warning.
2. RPC Read Actions (Queries): Instructed AI agents to export export const method = 'GET' for read-only RPC queries (await getTodos()) to enable URL search param passing, ETags, 304 revalidation, and export const cache = ... HTTP headers.
3. RPC Mutation Actions: Details usage of POST, PUT, PATCH, DELETE verbs with tag eviction (export const invalidates = (args...) => ['tag']).

Definition of Done Verification Checklist

• Unit tests: node --test packages/cli/test/**/*.js packages/cli/test/**/*.mjs test/scaffolds/scaffold-integration.test.js (84/84 pass)
• Convention check: ( cd examples/blog && npx webjs check ) && ( cd website && npx webjs check )
• Docs parity: website/app/docs/server-actions/page.ts updated

[vivek7405]

Review: HTTP verb guidance addition verified

Reviewed the updated skill reference documentation and website docs. The decision table and explicit rules clearly delineate form-bound POST actions vs RPC GET read queries and mutating verbs. All 84 unit and scaffold integration tests pass and webjs check is green.

[vivek7405]

Review: HTTP verb decision guide additions verified

The documentation updates clearly delineate form-bound POST actions vs RPC GET read queries and mutating verbs across .agents/skills/webjs/ and the website docs site. All 84 unit and scaffold integration tests pass and webjs check is green.