docs: complete explanation pages and expand guide and reference sections

[nikazzio]

Summary

• Rewrote three stub explanation pages (architecture, job-lifecycle, security-and-path-safety) from bullet placeholders to full prose, grounded in actual code behavior.
• Expanded four moderate pages (getting-started, first-manuscript-workflow, discovery-and-library, cli) with real features verified against source: wizard mode, download manager, acquisition granularity, path safety patterns, status machine.

Changes

File	Before	After
explanation/architecture.md	25 lines	97 lines
explanation/job-lifecycle.md	26 lines	106 lines
explanation/security-and-path-safety.md	15 lines	91 lines
getting-started.md	83 lines	122 lines
first-manuscript-workflow.md	81 lines	111 lines
discovery-and-library.md	103 lines	139 lines
reference/cli.md	55 lines	111 lines

All content verified against jobs.py, vault_jobs.py, utils.py, network_policy.py, cli.py, and route handlers. No new files; no code changes.

CI Checks

• check_docs_language.py — passed locally
• check_docs_integrity.py — passed locally
• markdownlint — passed locally

Related #66
Related #67

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.95%. Comparing base (ee55fa4) to head (66063b8).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #157      +/-   ##
==========================================
+ Coverage   70.93%   70.95%   +0.02%     
==========================================
  Files         153      153              
  Lines       13229    13229              
==========================================
+ Hits         9384     9387       +3     
+ Misses       3845     3842       -3     

Flag	Coverage Δ
fast	70.93% <ø> (ø)
slow	70.95% <ø> (+0.02%)	⬆️

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