feat(wasm-viewer): Save as Report works offline via shared report-save crate

The static-site WASM viewer's Save as Report button was POSTing to
`/api/v1/save_with_selection`. On rezolus.com (a static deployment
with no backend) the CDN returned 405 Method Not Allowed. Port the
trim + tarball-repack flow into a shared workspace crate so both the
server viewer and the WASM viewer run the same projection logic.

## Shared crate: `crates/report-save/`

Single source of truth for the trim/embed/tarball flow:
- `ReportPayload` / `ReportEntry` / `Side` payload types
- `resolve_kept_columns` (generic over `T: Deref<Target = Tsdb>`)
- `save_single_parquet(Bytes, …) -> Vec<u8>`
- `save_combined_ab_tarball(Bytes, Bytes, manifest_bytes: &[u8], …) -> Vec<u8>`
- All operating on `metriken_query::Bytes` — the unified primitive
  the server reads paths into and the WASM viewer already holds.
- 10 unit tests covering kept-column resolution + the full round-trip
  for both trim/no-trim and single/AB paths.

The shared crate is manifest-agnostic: it takes pre-serialized
manifest bytes for the AB tar entry, so it doesn't need to know about
either crate's `AbContainers` struct.

## Server-side shim: `src/viewer/report_save.rs`

Reads paths into `Bytes`, serializes the binary crate's `AbContainers`,
delegates to `report-save`. ~70 LOC (was ~250 LOC of trim logic + tests).

## WASM-side shim: `crates/viewer/src/report_save.rs`

Synthesizes an `AbContainers` manifest from the two attached viewers
(compare mode loads two separate parquets — there's no pre-existing
tar manifest), serializes it, delegates to `report-save`. The WASM
crate keeps its own `AbContainers` definition since it doesn't depend
on the rezolus binary crate.

`Viewer` now keeps the original parquet `Bytes` alongside the Tsdb so
the trim writer can project columns from the source schema (the Tsdb
has lost Arrow field metadata like the `metric` key that
`parquet filter`'s keep-field predicate needs).
`WasmCaptureRegistry::save_with_selection(payload_json)` dispatches
based on slot attachment.

## Unified JS surface

Both `site/viewer/lib/viewer_api.js` (WASM) and
`src/viewer/assets/lib/viewer_api.js` (server) expose
`saveWithSelection(payload) -> { bytes, mime, extension }`.
`saveToParquet` in `selection.js` calls through `ViewerApi` instead of
raw XHR — swaps the filename's `.parquet` suffix for the reported
extension so AB tarballs land as `*.parquet.ab.tar`.

## Cost

WASM bundle: 3.6 MB → 4.3 MB (parquet writer + tar). The `no_asm`
zstd-sys feature is target-scoped — resolver 2 doesn't propagate it
to `cargo build --bin rezolus`, so the standalone binary's zstd
keeps its x86 asm path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: thinkingfish

Cargo.lock

@@ -1,5 +1,5 @@
 [workspace]
-members = [".", "crates/dashboard", "crates/systeminfo", "crates/viewer"]
+members = [".", "crates/dashboard", "crates/report-save", "crates/systeminfo", "crates/viewer"]
 exclude = ["xtask"]
 resolver = "2"
 
@@ -21,13 +21,14 @@ serde = { version = "1.0.228", features = ["derive"] }
 serde_json = "1.0.149"
 thiserror = "2.0.18"
 dashboard = { path = "crates/dashboard" }
+report-save = { path = "crates/report-save" }
 include_dir = "0.7.4"
 walkdir = "2.5.0"
 wasm-bindgen = "0.2.120"
 
 [package]
 name = "rezolus"
-version = "5.13.1-alpha.6"
+version = "5.13.1-alpha.7"
 description = "High resolution systems performance telemetry agent"
 edition = "2021"
 license.workspace = true
@@ -121,6 +122,7 @@ tower-http = { version = "0.6.8", features = [
 ] }
 tower-livereload = "0.10.3"
 dashboard.workspace = true
+report-save.workspace = true
 systeminfo = { path = "crates/systeminfo" }
 walkdir.workspace = true
 tar = { version = "0.4.45", default-features = false }

Cargo.toml

@@ -0,0 +1,20 @@
+[package]
+name = "report-save"
+version = "0.1.0"
+edition = "2021"
+license.workspace = true
+repository.workspace = true
+homepage.workspace = true
+publish = false
+
+[lib]
+path = "src/lib.rs"
+
+[dependencies]
+arrow = "58.2.0"
+parquet = { version = "58.2.0", default-features = false, features = ["arrow", "simdutf8", "zstd"] }
+tar = { version = "0.4.45", default-features = false }
+serde.workspace = true
+serde_json.workspace = true
+metriken-query.workspace = true
+tracing = "0.1"