docs: launch-readiness pass for the local inference feature

[quiet-node]

Overview

Aligns every user-facing word in the repo with the shipped local inference feature for the v0.15.0 release. The bundled built-in engine is the zero-setup default, with Ollama as the optional provider. This pass corrects stale copy, fills the documentation gap, and refreshes the in-app tips.

What changed

In-app copy

• The model reasoning capability is named "Reasoning" consistently: the capability badge, the live streaming block ("Reasoning..." then "Reasoning"), the /think description, and the chat export.
• Residency wording is unified on "Keep Warm" and "in memory" (Apple Silicon shares unified memory, so there is no separate VRAM).
• The OCR-failure hint no longer says "via Ollama", the no-models cue drops "LLM", and onboarding no longer calls a model a "brain".

README

• Leads with the built-in zero-setup story and names the Settings > Models surfaces: Library, Discover (Staff picks and Browse all), and Providers, plus Keep Warm.
• Corrects the model-download pointer to Discover and the TypeScript badge.

Docs

• New guides: Models and providers, Privacy, and Troubleshooting, linked from the README.
• configurations.md, SECURITY.md, and the tuning and OCR guides are corrected for accuracy and made engine-agnostic. configurations.md drops the phantom MAX_IMAGES_PER_MESSAGE constant and documents the real, tunable image cap.
• SECURITY.md documents the local inference posture: a localhost-only sidecar with the web UI disabled, bounded GGUF parsing, and model provenance from pinned repo revisions.

Tips

• Stale Ollama tips are generalized to the built-in engine, with new tips for the model library, providers, vision, and reasoning.

Provider scope

• The OpenAI-compatible provider (its UI is behind a dev flag) is intentionally not mentioned in user-facing copy for this release. The loader still accepts an existing kind = "openai" config for back-compat.

Testing

bun run test:all:coverage (frontend 100%, 2075 tests; backend 100% lines) and bun run validate-build both pass.

Notes

The README's demo videos and logo show older UI and need a human recapture (visuals cannot be verified headless). The CHANGELOG's hand-written Unreleased block carries the BREAKING migration notes, so only its factual contradiction was corrected here; how release-please folds it into the 0.15.0 section is a release-engineering choice left to the release.