fix(sql): preserve execution context correctness

[openai0229]

Related issue

Closes #1869

Enterprise equivalent: OtterMind/Chat2DB-Enterprise#97, tracked by Enterprise Issue #95.

Summary

• Restore the database selected in the editor before each synchronous or streaming execution through the existing database-plugin abstraction and the same JDBC connection.
• Make Output context capture observational only, preserving native catalog/schema semantics such as PostgreSQL SET LOCAL, DEFAULT, and multi-target search_path.
• Preserve statement-start context on failure or cancellation, handle SQL Server GO batches correctly, bound Output record/message growth, and keep Community execution timing internally consistent.
• Prevent duplicate Desktop log events and message ID collisions without changing the SQL execution API.
• Route successful tabular Web executions to the newest result tab while keeping no-result, failed, and cancelled executions on Output. Mixed Web batches now fall back to the backend top-level statementSequence when structured stream metadata is absent.

Affected surfaces

• Frontend / Web
• Backend / API / Storage
• Database plugin / Driver
• JCEF / Desktop packaging
• CI / Build / Release
• Documentation only

Verification

• Commands and results:
  • cd chat2db-community-server && rtk mvn -q clean test install -Dmaven.test.skip=false -DskipTests=false: passed all 48 modules; 866 tests, 0 failures, 0 errors, 1 skipped.
  • cd chat2db-community-client && rtk yarn test:search-result-tab-selection: passed.
  • cd chat2db-community-client && rtk yarn test:sql-execution-log: passed.
  • Targeted ESLint for the five changed frontend files: passed.
  • cd chat2db-community-client && rtk yarn run build:web:community --app_version=5.3.0: passed.
  • rtk git diff --check: passed.
• Manual verification: Playwright CLI reproduced the old mixed-batch failure against local MySQL. After the correction, SELECT / SELECT / USE / SELECT activates the final result tab, a successful no-result USE activates Output, and a failed SELECT activates Output.
• UI evidence: Browser-verified on Community Web at the current development build; this changes active-tab routing without changing visual layout.

Risk and compatibility

• Public API or stored data: No public API, schema, or persisted-data migration.
• Database or driver compatibility: Execution-start session alignment and SQL Server batch handling change intentionally; focused tests pass. Local MySQL Web smoke passed, while real PostgreSQL and SQL Server driver smoke remains the residual risk.
• Network, privacy, or security: N/A; no network boundary or credential handling changes.
• Community / Local / Pro boundary: This PR contains the Community implementation. Equivalent Enterprise behavior is under review in Enterprise PR 建议: ssh支持密钥登录 #97; enterprise-migration is intentionally unchanged.
• Backward compatibility: Corrects session/context and result-tab behavior without a compatibility fallback or migration.

Reviewer map

• Start here: DefaultSQLExecutor, JdbcExecutionContext, and SqlServerExecutor; then review sqlExecutionLog.ts for bounded frontend state and event deduplication. For result routing, review SQLExecute, SearchResult, tabSelection.ts, and sortExecutionResults.
• Failure condition: A statement executes outside the editor-selected database, Output reports a context different from the JDBC session, GO reaches the driver, final status/timing is lost when records are bounded, or a successful batch ending in a tabular result leaves Output active.
• Rollback or disable path: Revert this PR; there is no data migration or feature flag.

Contributor declaration

• I linked the Issue that defines this change.
• I tested the affected behavior and reported the actual results above.
• I did not include credentials, private data, or generated build output.
• I disclosed substantial AI assistance below, or this PR contains no substantial AI-generated code.

AI assistance: Substantial AI assistance was used for implementation, regression tests, browser verification, and cross-repository review.

[openai0229]

Cancellation follow-up

This PR now also fixes the persistent Unknown Error banner shown after an intentional Web query cancellation.

• A confirmed transport cancellation still records cancelled, keeps Output active, and restores the previous result snapshot when needed.
• The cancellation is no longer propagated to the SQL editor error banner.
• Non-cancellation errors continue to propagate unchanged.
• Classification is limited to structured AbortError, CanceledError, and ERR_CANCELED markers; PostgreSQL current transaction is aborted remains a real error.

Verification:

• Playwright CLI: cancelling SELECT SLEEP(10) AS slept; produces Execution cancelled with zero Unknown Error banners.
• test:sql-execution-log: passed in Community and Enterprise.
• Targeted ESLint: passed in Community and Enterprise.
• Web production build: passed in Community and Enterprise.
• git diff --check: passed in Community and Enterprise.