fix(fastly): apply canonical store selectors at deploy

[aram356]

Summary

• Restore the pre-Support optional typed secret paths and Fastly store mappings #344 Fastly runtime-selector model so canonical EDGEZERO__STORES__... variables from the deployer's selected GitHub Environment control each deployment.
• Remove service-scoped selector variables and EDGEZERO_FASTLY_BUILD_SETTINGS while retaining optional typed secret paths from Support optional typed secret paths and Fastly store mappings #344.
• Let production and staging select the same or different Config, KV, and Secret Stores without adding Fastly-specific flags or branching to the generic CLI.

Changes

Crate / File	Change
edgezero-adapter / edgezero-cli	Add an adapter-neutral typed deploy context and deploy/finalize hooks; custom and built-in deploys share the same lifecycle and fail before activation when required finalization is unavailable.
edgezero-adapter-fastly	Read canonical selectors from edgezero_runtime_env, reconcile production selectors after deploy, and use one per-service staging twin linked to the staged draft. Staging also links each selected physical Config, KV, and Secret Store.
GitHub Actions	Remove the build-settings payload and service-scoped environment mapping; pass the selected service/environment through the normal deploy interface.
Documentation	Document deploy-time selection, production/staging sharing or isolation, provisioning responsibilities, and canonical variable names.
Tests	Cover canonical secret selection, same/different staging stores, custom deploy finalization, explicit manifest targeting, FASTLY_SERVICE_ID fallback, optional secrets, and action-script behavior.

Deploys remain serialized per Fastly service. If an operator deletes or mutates a selected resource during a deploy, the provider operation fails clearly; this change does not introduce version-specific selector stores or recovery machinery for concurrent external mutation.

Closes

Closes #380

Test plan

• cargo test --workspace --all-targets
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• cargo fmt --all -- --check
• cargo check --workspace --all-targets --features "fastly cloudflare spin"
• WASM builds: wasm32-wasip1 (Fastly) / wasm32-wasip2 (Spin) / wasm32-unknown-unknown (Cloudflare) — verified cargo check -p edgezero-adapter-spin --target wasm32-wasip2 --features spin
• examples/app-demo workspace: cd examples/app-demo && cargo test --workspace --all-targets
• Docs build: cd docs && npm run lint && npm run format && npm run build
• Manual testing via edgezero serve --adapter axum (the pre-rewrite edgezero-cli dev was renamed; see cli-reference)
• Other: .github/actions/deploy-core/tests/run.sh (263 passed, 0 failed, 4 platform skips); git diff --check

Checklist

• Changes follow CLAUDE.md conventions
• No Tokio deps added to core or adapter crates
• Route params use {id} syntax (not :id)
• Types imported from edgezero_core (not http crate)
• Store wiring goes through KvRegistry / ConfigRegistry / SecretRegistry (not the legacy single-handle setters) — see spec §6.6
• New code has tests
• No secrets or credentials committed