Use inline :exclude in josh-proxy URL instead of stored filter files

The :+ stored filter syntax doesn't work in josh-proxy URLs.
Inline :exclude[::p1,::p2] works directly — no files to generate
or commit, no extra dependencies.

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

docs/guide.md

@@ -541,19 +541,13 @@ targets:
 
 ### How it works
 
-When `exclude` is present, josh-sync generates a `.josh-filter-<target>.josh` file at the monorepo root containing a [josh stored filter](https://josh-project.github.io/josh/reference/filters.html) with `:exclude` clauses:
+When `exclude` is present, josh-sync appends an inline `:exclude` filter to the josh-proxy URL. For the example above, the josh filter becomes:
 
 ```
-:/services/billing:exclude[
-  ::.monorepo/
-  ::**/internal/
-  ::*.secret
-]
+:/services/billing:exclude[::.monorepo/,::**/internal/,::*.secret]
 ```
 
-The file is referenced in the josh-proxy URL as `:+.josh-filter-<target>` (flat naming — josh-proxy's parser treats `/` in `:+` paths as a filter separator, so subdirectory paths don't work).
-
-Josh-proxy reads this file from the monorepo and applies the filter at the transport layer. This means:
+Josh-proxy applies this filter at the transport layer — no extra files to generate or commit. This means:
 - **Forward sync**: the filtered clone already excludes the files
 - **Reverse sync**: pushes through josh also respect the exclusion
 - **Reset**: the subrepo history never contains excluded files
@@ -574,11 +568,10 @@ Josh uses `::` patterns inside `:exclude[...]`:
 ### Setup
 
 1. Add `exclude` to the target in `.josh-sync.yml`
-2. Run `josh-sync preflight` — this generates `.josh-filter-<target>.josh`
-3. Commit the generated file: `git add .josh-filter-*.josh && git commit`
-4. Forward sync will now exclude the specified files
+2. Run `josh-sync preflight` to verify the filter works
+3. Forward sync will now exclude the specified files
 
-If you change the `exclude` list, re-run `preflight` and commit the updated `.josh-filter-*.josh` file.
+No extra files to generate or commit — the exclusion is embedded directly in the josh-proxy URL.
 
 ## Adding a New Target