doc: simplify all AGENTS.md & update memories

[bitflicker64]

Visual summary

Purpose of the PR

Agent guidance repeated generic instructions and stale repository details across six files.
Documentation requirements also disagreed between AGENTS.md, the PR template and the contribution guide.

Main changes

• Reduce all six AGENTS.md files to fewer than 100 lines while keeping component relationships,
  common commands and repository-specific pitfalls inline. Link detailed POM, CI and deployment references.
• Require user-visible feature, configuration and deployment changes to ship with matching documentation.
  In-repository docs belong in the same PR; website changes use a paired hugegraph-doc PR.
  Doc - TODO means pending before merge, and a follow-up issue alone does not satisfy the requirement.
• Correct stale Serena notes for deployment topology, distribution output, compiler targets and test scope.
• Update README navigation without imposing a repository-wide prose reflow.

Validation

• Independent read-only review of the final diff: no remaining substantive findings.
• All six AGENTS.md files are under 100 lines; their local links resolve.
• git diff --check passed.
• Documentation-only change; no runtime tests executed.

Documentation Status

• Doc - TODO: synchronize the website contribution guidelines before merging.
• Doc - Done
• Doc - No Need

Documentation in this PR: AGENTS.md, module AGENTS.md files, docs/CONTRIBUTING.md,
README.md, the PR template and Serena notes.
Paired hugegraph-doc PR: pending.

Related repositories may adopt the policy separately; their full PR templates are not byte-identical.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 41.13%. Comparing base (e85b36a) to head (899f072).
⚠️ Report is 8 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3197      +/-   ##
============================================
+ Coverage     37.79%   41.13%   +3.34%     
- Complexity     6563     7212     +649     
============================================
  Files           800      802       +2     
  Lines         68960    69393     +433     
  Branches       9166     9237      +71     
============================================
+ Hits          26061    28546    +2485     
+ Misses        39834    37585    -2249     
- Partials       3065     3262     +197     

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[bitflicker64]

Blocking: no. Summary: The design-philosophy section and the doc-sync paragraph are additive and read well, but the three edited files disagree about what the rule actually is, and the README guidance does not match the README it describes. Separately, open point 2 in the description says the PR template is byte identical in hugegraph-toolchain and hugegraph-computer; it is not (the Documentation Status block is identical, the rest of the file differs in several places), so that follow-up is a hand merge rather than a copy. Evidence: git show 96a48ad:.github/PULL_REQUEST_TEMPLATE.md, AGENTS.md, docs/CONTRIBUTING.md and README.md at head; awk 'length>120' README.md returns 47 lines, including prose; diff of .github/PULL_REQUEST_TEMPLATE.md fetched via gh api from apache/hugegraph, apache/hugegraph-toolchain and apache/hugegraph-computer default branches.