Docs: lean-pass rewrite of the user manual + succinct tone guidance

[brickbots]

What

A "warm but lean" pass across all nine reader-facing documentation pages, plus an update to the docs skill's house-voice guidance that codifies the new direction.

The goal: keep the manual's warm, direct "you" voice, but cut the padding so it reads tighter at the eyepiece. ~14% fewer words (≈3,100 cut) with every image, cross-reference, note, and caveat preserved.

Pages leaned

Page	Words
quick_start	4075 → 3265 (20%)
user_guide	6114 → 5312 (13%)
build_guide	6247 → 5604 (10%)
catalogs	488 → 422 (14%)
v25_upgrade	1056 → 880 (17%)
software	1036 → 936 (10%)
skysafari	740 → 641 (13%)
equipment	1078 → 1003 (7%)
troubleshooting	2098 → 2008 (4%)

Lighter trims (build_guide, software, troubleshooting, equipment) are expected — those pages are mostly steps, measurements, commands, and symptom→fix checks, so only prose padding came out.

Kinds of changes

• Cuts: throat-clearing ("In order to…", "It is important to note…"), redundant restatement, and hedging. The why is kept but compressed to a clause; longer asides moved into .. note::.
• Structure: multi-step procedures became numbered lists where images don't interleave the steps (kept as bullets where they do, since rST restarts numbering after each image).
• Tone guidance: added a "Be succinct" principle and reframed "explain the why" → "compress the why" in .claude/skills/docs/SKILL.md.

Bonus fixes caught along the way

• Repaired a broken :doc: cross-reference in user_guide.rst that was split across a line break (rendered as literal text).
• Fixed skysafari.rst heading hierarchy — sections were all top-level siblings of the title; now proper subsections.
• Assorted its/it's, philips→Phillips, PCB's→PCBs, a port-value self-contradiction in skysafari, double spaces.

Notes for reviewers

• The user_guide pass was re-run on top of the newly merged Power & Charging / LiPo safety section (Docs: add Power & Charging section to user guide (incl. LiPo safety) #447) — that section and its safety warnings are preserved in full and leaned alongside the rest.
• No toctree or page renames; heading levels and underline characters unchanged (except the intentional skysafari fix).

Verification

• sphinx-build -b html -n -E is clean — no warnings on any touched page (only the pre-existing repo-wide _static path warning remains).
• Image/figure/:ref:/:doc: counts verified equal to origin/main for every page (the single :doc: delta in user_guide is the broken-link repair above).

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