Remove temporary tool preview feature flag

[gandhipratik203]

Summary

This removes the temporary VITE_ENABLE_TOOL_PREVIEW flag and makes the Tools details drawer always render the Try it / Definition tab layout.

Changes:

• remove the tool-preview feature helper
• always open Tools details on Try it
• remove test env stubs and the obsolete false-flag test
• remove Playwright, Dockerfile, and docker-compose.e2e flag wiring
• remove the now-empty ImportMetaEnv block

Context

• Closes Remove temporary tool preview feature flag after backend preview endpoint lands IBM/mcp-context-forge#6322.
• Refs [UI-REWRITE]: Add preview experience to ToolDetailsPanel IBM/mcp-context-forge#5630.
• Depends on [FEATURE][API]: Add tool preview endpoint for safe invocation dry-run IBM/mcp-context-forge#5629.
• Builds on merged PR Add gated tool live invocation and snippets #79, where live invoke also rode the same Try-it feature flag.

Blocker

This PR is intentionally draft-only until the backend preview endpoint lands.

Removing the flag flips the production/default image path from Try-it hidden to Try-it visible. Since /rpc exists but /tools/preview/{name} does not until IBM/mcp-context-forge#5629 lands, the post-removal production state would expose gated live invoke beside a Preview button that 404s.

The current docker e2e gateway image is ghcr.io/ibm/mcp-context-forge:v1.0.8, which predates the preview endpoint.

Un-draft Gate

• [FEATURE][API]: Add tool preview endpoint for safe invocation dry-run IBM/mcp-context-forge#5629 is merged.
• docker-compose.e2e.yml is bumped to the first ghcr.io/ibm/mcp-context-forge release containing POST /tools/preview/{name}.
• npm run e2e:docker passes against that image.
• Manual verification confirms both Preview and Live invoke from the default Tools Try-it tab.

Tests

• git grep -n "VITE_ENABLE_TOOL_PREVIEW\|isToolPreviewEnabled" -- . - no tracked matches
• npm run lint
• npm run format:check
• ./node_modules/.bin/tsc -b
• npm run test
• npm run build
• PLAYWRIGHT_SKIP_WEBSERVER=1 PLAYWRIGHT_BASE_URL=http://127.0.0.1:5173 npm run e2e -- e2e/tools.spec.ts -g "previews a tool|live invokes|confirms destructive|cancellation|tools.execute|servers.use|federated|denied passthrough"
• git diff --check

Not Run

• npm run e2e:docker - blocked until the pinned gateway image contains [FEATURE][API]: Add tool preview endpoint for safe invocation dry-run IBM/mcp-context-forge#5629.

Manual Verification

Pending real-backend verification. The UI can now expose the default Try-it tab without setting VITE_ENABLE_TOOL_PREVIEW, but the real Preview action must not be signed off until the backend endpoint exists in the tested gateway image.