Add feature installer script for L&L-compatible installs

Provides an alternative install method where users run a script on a
standard Loop clone after applying any L&L customizations. The script
uses anchor-based text insertion and 3-way merges to adapt to whatever
patches are already present, making all L&L customizations compatible.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: taylorpatterson-T1D

INSTALL.md

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+# Install FoodFinder + LoopInsights + AutoPresets
+
+Add AI-powered food analysis, therapy settings insights, and automatic preset management to your Loop app — compatible with Loop & Learn customizations.
+
+## Prerequisites
+
+- **Xcode 15+** (15.4 recommended)
+- **iOS 17+** on your target device
+- **macOS** with git and python3 (both ship with Xcode Command Line Tools)
+- **API key** for AI features (OpenAI, Anthropic, or Google — configured in-app after install)
+
+## Step 1: Clone LoopWorkspace
+
+Follow the standard Loop build instructions:
+https://loopkit.github.io/loopdocs/build/step4/
+
+```bash
+git clone --branch=main --recurse-submodules https://github.com/LoopKit/LoopWorkspace
+cd LoopWorkspace
+```
+
+## Step 2: Apply Loop & Learn Customizations (Optional)
+
+If you want L&L customizations (Profiles, Basal Lock, Negative Insulin, etc.), apply them **before** running the feature installer:
+
+https://www.loopandlearn.org/custom-code/
+
+All L&L patches are compatible with our features. The installer automatically adapts to whatever patches are present.
+
+## Step 3: Install Features
+
+From the LoopWorkspace root directory:
+
+```bash
+/bin/bash Scripts/install_features.sh
+```
+
+Or, if you haven't cloned this repository yet:
+
+```bash
+curl -fsSL https://raw.githubusercontent.com/TaylorJPatterson/LoopWorkspace/feat/installer/Scripts/install_features.sh -o /tmp/install_features.sh
+curl -fsSL https://raw.githubusercontent.com/TaylorJPatterson/LoopWorkspace/feat/installer/Scripts/update_pbxproj.py -o Scripts/update_pbxproj.py
+/bin/bash /tmp/install_features.sh
+```
+
+The script will:
+1. Validate your environment
+2. Back up your current state (git stash)
+3. Fetch the feature source code
+4. Install 77 new files and patch 11 existing files
+5. Update the Xcode project file
+6. Validate everything
+
+## Step 4: Build in Xcode
+
+1. Open `LoopWorkspace.xcworkspace` in Xcode
+2. Select your signing team
+3. Build and run (Cmd+R)
+
+## Step 5: Enable Features in Settings
+
+All features are **off by default**. Enable them in the Loop app:
+
+- **FoodFinder**: Settings → FoodFinder → Toggle on. Enter your AI API key.
+- **LoopInsights**: Settings → LoopInsights → Toggle on. Same API key is shared.
+- **AutoPresets**: Settings → AutoPresets → Configure motion detection and preset rules.
+
+## Updating
+
+To update to the latest feature version:
+
+1. Run the rollback: `./Scripts/install_features.sh --rollback`
+2. Re-run the installer: `./Scripts/install_features.sh`
+
+## Uninstalling
+
+```bash
+./Scripts/install_features.sh --rollback
+```
+
+This removes all feature files and restores your Loop to its pre-install state (including any L&L patches you had applied).
+
+## L&L Compatibility
+
+| L&L Customization | Compatible | Notes |
+|---|---|---|
+| Profiles | Yes | Our features insert below Profiles in Settings |
+| Basal Lock | Yes | Different code regions than our features |
+| Negative Insulin | Yes | Different code regions than our features |
+| Future Carbs 4h | Yes | Both modify CarbEntryView.swift but in different regions; 3-way merge handles it |
+| Override Insulin Needs Picker | Yes | No overlapping files |
+| All other L&L patches | Yes | Our installer only modifies Loop submodule files |
+
+## Troubleshooting
+
+**"Anchor not found" error**: Your Loop version may be too old or too new. The installer targets Loop dev branch (v3.10.x). Make sure you cloned the latest LoopWorkspace.
+
+**Merge conflicts during patching**: If the installer reports conflicts, check the affected file for `<<<<<<<` conflict markers and resolve them manually.
+
+**Xcode build errors after install**: Try a clean build (Cmd+Shift+K, then Cmd+R). If issues persist, run `--rollback` and re-install.
+
+**plutil validation failure**: The Xcode project file update failed. The installer automatically restores the backup. Try again — if it persists, file an issue.