fix(storage): preserve tree on invalid or failed moves

[HandSonic]

Related issue

N/A - this defect was found during review of local tree storage moves; no public issue currently tracks it.

Summary

• Keep the stored tree unchanged when a move targets a missing node, itself, or a descendant.
• Persist a candidate tree before publishing tree moves or tree-node deletions in memory.
• Preserve normal group and datasource creation through a separate internal insertion path; existing-node moves retain their validation.

This PR is limited to tree operations and their direct creation regression. General record-storage rollback, cross-file transactions, and retry/idempotency changes are excluded.

Affected surfaces

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

Verification

• Local storage reactor tests and package passed: storage 79, domain-api 27, tools 77; 183 tests total, zero failures/errors/skips.
• Command: mvn -B -ntp -f chat2db-community-server/pom.xml -pl :chat2db-community-storage -am -Dmaven.test.skip=false -DskipTests=false '-Dsurefire.includes=**/*Test.java' -Dsurefire.failIfNoSpecifiedTests=false -Dmaven.test.failure.ignore=false package. Test JVMs used isolated temporary home and temp directories.
• Fresh Playwright CLI checks on the simplified build passed: root/nested group creation, refresh, real mouse drag, menu moves with descendants, missing/self/descendant/missing-source no-ops, real tree-directory write denial with unchanged memory and disk, backend restart, delete cancellation with zero writes, and child promotion after deletion.
• Regression tests also cover all four supported drop positions, ID-only namespace moves preserving children, normal datasource insertion, and tree reload.
• Simplify tree persistence and insertion branches, remove the artificial delay, and avoid duplicate tree copies for mutations that already own a detached candidate.
• New-head CI is triggered by this update; its current result is available in PR checks.

Risk and compatibility

• Public API and tree JSON format remain unchanged. New-node insertion is an internal storage entry point.
• Normal creation must not be rejected by the existing-source move guard. Regression tests exercise actual LocalWorkspaceStorage callers.
• Failure preservation applies to the tree's own state/file. Datasource/namespace record files are not part of an atomic transaction with the tree; this PR does not claim to repair their pre-existing cross-file failure behavior.
• No database-driver, network, credential, runtime-registration or packaging changes.

Reviewer map

• Reviewer: @openai0229 (default CODEOWNER for community storage).
• Start here: TreeNodeStorage.updatePosition, createTree / persistTree, then the invalid-target and forced-replacement-failure cases in TreeNodeStorageTest.
• Failure condition: A missing, self, or descendant target, or an atomic replacement exception, must leave both the in-memory and reloaded tree unchanged; a valid move must still be visible in both.
• Rollback or disable path: Revert the PR as a whole; there is no runtime flag because this restores storage consistency.

Contributor declaration

• I linked the Issue that defines this change. (N/A - no public issue exists.)
• 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, tests, and adversarial review; the resulting diff and test evidence were manually inspected.