[feature]: Retire `proof.Archiver.ImportProofs` in favour of the verified-import pattern

Nobody has claimed this yet.

The `proof.Archiver` interface currently requires an `ImportProofs` method that accepts a `VerifierCtx` argument, implying verification will occur before storage. In practice, most implementations ignore this argument:

- **`proof.FileArchiver.ImportProofs`** (`proof/archive.go:738`) — ignores the `VerifierCtx` entirely (parameter is `_`), writing proofs directly to disk with no verification.
- **`tapdb.AssetStore.ImportProofs`** (`tapdb/assets_store.go:2049`) — also ignores the `VerifierCtx`, inserting proofs into the database without verification.
- **`proof.MultiArchiver.ImportProofs`** (`proof/archive.go:1004`) — the only implementation that actually verifies proofs before delegating to its backends.

This inconsistency is misleading. Callers pass a `VerifierCtx` believing verification will happen, but depending on the archiver wired in, it may be silently skipped.

Meanwhile, a **verified-import pattern** has been introduced: callers explicitly verify proofs via `proof.VerifyAnnotatedProofs()` to obtain `VerifiedAnnotatedProof` values, then call `ImportVerifiedProofs()` which stores without re-verification. `ChainPorter.storeProofs` already uses this pattern. This is clearer and safer because verification is explicit at the call site rather than hidden (or not) inside the archiver.

### Proposal

1. **Remove `ImportProofs` from the `proof.Archiver` interface** (`proof/archive.go:198`).

2. **Add `ImportVerifiedProofs` to the `proof.Archiver` interface** (or a new composed interface) so all archivers accept only pre-verified proofs.

3. **Remove proof verification from `MultiArchiver.ImportProofs`** and replace the method with `ImportVerifiedProofs`. The `MultiArchiver` should no longer hold a `proofVerifier` field; verification is the caller's responsibility.

4. **Add `ImportVerifiedProofs` to `tapdb.AssetStore`**, following the same pattern as `FileArchiver.ImportVerifiedProofs` — unwrap the `VerifiedAnnotatedProof` values and delegate to the internal storage logic.

5. **Migrate all call sites** from `ImportProofs` to the verified-import pattern (`proof.VerifyAnnotatedProofs` → `ImportVerifiedProofs`):

| Call site | File | Line |
|-----------|------|------|
| `rpcServer.ImportProof` (dev RPC) | `rpcserver.go` | 2339 |
| `rpcServer.ProveFetchedAssetProvenance` | `rpcserver.go` | 10659 |
| `Custodian` (address proof import) | `tapgarden/custodian.go` | 934 |
| `Custodian` (non-interactive proof import) | `tapgarden/custodian.go` | 1567 |
| `ReOrgWatcher` (updated proof re-import) | `tapgarden/re-org_watcher.go` | 633 |
| `BatchCaretaker` (minting proof storage) | `tapgarden/caretaker.go` | 1219 |
| `ChainPlanter` (updated proof re-import) | `tapgarden/planter.go` | 3121 |
| `AuxSweeper` (funding proof import) | `tapchannel/aux_sweeper.go` | 1526 |

6. **Update tests** that call `ImportProofs` directly (in `proof/archive_test.go`, `tapdb/assets_store_test.go`, `tapdb/sqlutils_test.go`) to use the new API.

7. **Remove the `proofVerifier` field from `MultiArchiver`** and simplify its constructor since verification is no longer its concern.

### Notes

- The `ChainPorter` already follows the verified-import pattern (`chain_porter.go:528-539`, `chain_porter.go:620-635`) and uses the `VerifiedProofImporter` interface, so it requires no changes.
- Each migrated call site should call `proof.VerifyAnnotatedProofs(ctx, vCtx, ...)` before import. Since every existing call site already constructs and passes a `VerifierCtx`, the verification context is readily available.
- This change makes it impossible to accidentally import unverified proofs — the type system enforces that `ImportVerifiedProofs` only accepts values produced by the verification step.

Start with the proof.Archiver interface and implementations in proof/archive.go, then compare FileArchiver.ImportVerifiedProofs with the verified-import flow in chain_porter.go. Migrate the listed rpcserver.go, tapgarden, and tapchannel call sites, add the tapdb.AssetStore method, and update tests in proof/archive_test.go, tapdb/assets_store_test.go, and tapdb/sqlutils_test.go. Done means ImportProofs and MultiArchiver verification are removed and the affected tests pass.

Written by the indexing model from the issue text.