Build FlexDoc 2.9 API Client execution, IntelliSense, and full history

[bluejeans117]

Summary

• extract API Client request execution into a reusable canonical executor shared by normal sends and collection execution
• add collection-runner sequencing on top of the same request, auth, script, and variable engine
• add dependency-free scripting IntelliSense for the flex.* runtime, including dot/Ctrl+Space completion, signatures, documentation, assertion-chain help, and known variables
• promote request history from the compact recent list to a searchable and filterable full-page inspector with replay, deletion, response details, tests, logs, and preserved collection/folder provenance
• persist response headers and bounded response bodies for new history entries while remaining compatible with existing workspace data
• synchronize committed adapter renderer assets with the canonical 2.9 standalone build

Validation

• client lint
• complete client unit suite
• canonical client/standalone build
• adapter asset parity
• full Chromium/Playwright renderer suite
• exact-head repository CI and complete adapter matrix all passed

Compatibility

• API Client workspace persistence remains backward-compatible; new history response fields are optional
• older history entries remain readable even when they do not contain captured response payloads
• history entries whose originating collection or folder was deleted retain explicit provenance labels and remain replayable through the current workspace fallback