Standardize error handling across sync and upload paths

## Problem

Error handling is inconsistent across the codebase:

1. **Swallowed exceptions** — Some uploaders catch `Exception`, log a message, but don't propagate the error, causing silent failures in critical sync paths
2. **Bare `catch(Exception)`** — Used extensively (~103 try-catch blocks) instead of catching specific exception types
3. **Inconsistent logging context** — Some places log full stack traces, others just the localized message
4. **No structured error types** — Errors are communicated as strings or swallowed entirely rather than using Result types or sealed classes

## Key Locations

- `TreeUploader.kt` — `windowedTreeUpload()` catches and swallows all exceptions
- `PlanterUploader.kt` — silent failures in upload steps
- `TreeSyncWorker` — `doWork()` body lacks comprehensive error wrapping
- `MessagesRepo.kt` — mix of proper CancellationException re-throw and bare catches
- Various repositories — inconsistent error context in Timber logs

## Suggested Fix

1. Replace bare `catch(Exception)` with specific exception types where possible (e.g., `IOException`, `HttpException`)
2. Always re-throw `CancellationException` in coroutine contexts
3. Consider introducing a `Result` or sealed class pattern for error propagation
4. Standardize Timber logging to always include the exception object: `Timber.e(exception, "message")`
5. Ensure sync failures are visible to the user or retry mechanism

## Effort
High — touches many files, but can be addressed incrementally per module.