docs: refresh r/PowerShell launch draft to v1.21.1 ground truth (000095)

[manderse21]

Doc-only refresh of the held r/PowerShell launch draft (docs/launch/reddit-powershell.md) from stale v1.19.0 framing to v1.21.1 ground truth. Dispatch 000095.

Three load-bearing corrections

• Release framing: dropped "New in this release: SARIF" (that was v1.19.0). SARIF / CI-scan stays as an existing capability; the "new" slot is now the v1.21.0/v1.21.1 ruleset story.
• Rules section: replaced the "exactly six / Write-Host NOT surfaced" framing with lean-by-default + opt-in ruleset=base (54 enumerated rules, incl. PSAvoidUsingWriteHost and the three Error-severity security rules), curated 57 -> 54 via the 000091/000092 evidence survey.
• Settings line: replaced the false "settings can't add a rule PSES doesn't run live" with the truth -- a resolved PSScriptAnalyzerSettings.psd1 (or settingsPath) REPLACES the live rule set and can narrow OR broaden; the ruleset knob only applies when none resolves.

Verified from disk (no count carried forward unverified)

• Default surface: "about 15 rules, of which roughly six fire on everyday code" -- the ~15 ceiling from plugin.json userConfig + README (ruleset tiers); the measured six from the README corpus section + dispatch 000085.
• base ruleset: 54 enumerated rules -- rulesets/base.psd1 (counted) + CHANGELOG v1.21.1.
• Version: v1.21.1 (tagged) -- plugin.json + CHANGELOG.

Scope / holds

• One file only (explicit pathspec); no code/ruleset/manifest change, no version bump, no CHANGELOG entry.
• ASCII-clean, no-BOM; bare-subject commit authored by Mike Andersen.
• HELD for Mike's merge. Posting to Reddit remains Mike's gate -- please do not merge or post on my behalf.

🤖 Generated with Claude Code

https://claude.ai/code/session_01U4njWhC5kqaicXKn4Ve9KC