Add drawer body font size setting and update defaults

[BobDLA]

Summary

• add a persisted body font size slider to the drawer settings and apply it to post body and code blocks
• change the default drawer options to iframe preview, full topic, 15px body text, all authors, default order, floating reply off, overlay mode, and narrow width
• update smoke coverage and docs so preview-mode-sensitive cases set up their own scenario explicitly
• ignore the local temp directory in .gitignore

Verification

• bash scripts/check.sh
• bash scripts/agent-smoke.sh --cdp-port 9222 --cases AGENT-CHROME-001,AGENT-CHROME-002,AGENT-CHROME-003,AGENT-CHROME-004,AGENT-CHROME-005,AGENT-CHROME-006,AGENT-CHROME-008,AGENT-CHROME-009,AGENT-CHROME-010,AGENT-CHROME-016

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Hide or disable the body font-size slider in iframe mode

This new control is shown unconditionally, but on a fresh install previewMode now defaults to "iframe" in DEFAULT_SETTINGS, and the slider only feeds the --ld-post-body-font-size CSS variable that is consumed by .ld-post-body in smart preview. In the default configuration there is no .ld-post-body at all—loadTopic() renders an <iframe> instead—so the new setting appears broken until the user discovers they must switch preview modes first.

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