Speed up root access on the node read and create paths

[rymsha]

Performance of the two hottest root-node touches, plus a behaviour pin. Four commits:

1. Pin node create behaviour for missing repository and branch — NodeServiceImplTest covered getById against a missing repository and branch but not create, leaving the exception it reports unspecified. The pin comes first so the next commit demonstrably changes nothing observable.
2. Verify the branch on the node create path only when it fails — every node service method verified branch existence up front, which for create meant a storage lookup of the root node on top of the parent it reads anyway. The lookup now happens only once a parent turns out to be missing, where it tells a missing branch from a missing parent; a missing repository keeps being reported as such rather than as the index error underneath. The guard moves to NodeHelper so the service and the create command share one copy.
3. Answer the root path from the node id it always has — resolving a path asks the branch index which node holds it, and caches the answer; the root path needs neither, since the root node keeps the one id known without lookup and can be neither moved nor deleted. Previously an uncached root path refreshed the storage index and searched it, and a cached one resolved inside the path cache's atomic block — serializing every concurrent lookup of the busiest path in the repository across a storage round trip.
4. Drop javadoc from internal node and branch methods — cleanup on the internals the two changes touched.

An earlier revision also fixed resolvePotentialManualOrderValue ignoring a manually ordered root; that fix is deliberately dropped from this PR — legacy manual ordering under root stays as it was, and root ordering is handled by the order-key work in #12285 instead.

🤖 Generated with Claude Code

https://claude.ai/code/session_01ANkY5TN9xn2cFKHk1sfX4B

[codacy-production]

Codacy's Analysis Summary

0 new issue (≤ 0 issue)
0 new security issue
0 complexity
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[Copilot]

Pull request overview

Updates node creation to assign manual order values under manually ordered roots and centralizes repository/branch validation.

Changes:

• Removes the root exclusion from manual order resolution.
• Refactors branch validation and root lookups.
• Adds regression tests for ordering and invalid contexts.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
modules/itest/itest-core/src/test/java/com/enonic/xp/core/node/NodeServiceImplTest.java	Tests missing repository and branch handling.
modules/itest/itest-core/src/test/java/com/enonic/xp/core/node/CreateNodeCommandTest.java	Tests manual ordering under a root node.
modules/core/core-repo/src/main/java/com/enonic/xp/repo/impl/node/NodeServiceImpl.java	Delegates branch validation.
modules/core/core-repo/src/main/java/com/enonic/xp/repo/impl/node/NodeHelper.java	Centralizes branch validation.
modules/core/core-repo/src/main/java/com/enonic/xp/repo/impl/node/CreateNodeCommand.java	Resolves manual order values for root children.
modules/core/core-repo/src/main/java/com/enonic/xp/repo/impl/branch/storage/BranchServiceImpl.java	Supports root lookups by ID.

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[codecov]

Codecov Report

❌ Patch coverage is 90.47619% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.02%. Comparing base (b0341bd) to head (0193375).

Files with missing lines	Patch %	Lines
.../java/com/enonic/xp/repo/impl/node/NodeHelper.java	80.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master   #12283   +/-   ##
=========================================
  Coverage     87.01%   87.02%           
- Complexity    20754    20758    +4     
=========================================
  Files          2593     2593           
  Lines         69055    69063    +8     
  Branches       5723     5723           
=========================================
+ Hits          60091    60100    +9     
  Misses         6290     6290           
+ Partials       2674     2673    -1     

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