feat: add contract deployment validation

[Stanley-Owoh]

Add contract deployment parameter validation

Closes #285

Summary
Adds typed, fail-fast validation of deployment parameters at initialization
time for the payroll and payment_executor contracts. Mis-wired
deployments (duplicate dependency addresses, self-references, role/dependency
collisions) now fail at initialize with a typed DeploymentError instead of
silently producing a broken deployment that only surfaces at first payment.

Also introduces an optional, admin-gated, one-time network identifier on the
payroll contract for multi-network deployments (testnet/mainnet QA).

Changes
payroll contract (contracts/payroll/src/lib.rs)
New DeploymentError contract error enum:
AlreadyInitialized = 1
DuplicateDependency = 2
RoleConflictsWithDependency = 3
SelfReference = 4
NotInitialized = 5
NetworkIdAlreadySet = 6
InvalidNetworkId = 7
initialize(admin, token, verifier, commitment, treasury, treasury_owner)
now returns Result<(), DeploymentError> and validates before writing any
state:
no dependency may point at the payroll contract itself (SelfReference)
token / verifier / commitment must be pairwise distinct
(DuplicateDependency)
admin, treasury, and treasury_owner must not collide with a dependency
address (RoleConflictsWithDependency)
New one-time network identifier:
set_network_id(admin, network_id) — admin-gated, stores a non-empty
string of at most MAX_NETWORK_ID_LEN (128) bytes, emits a
network_id_set event; rejects repeats with NetworkIdAlreadySet and
over-long/empty values with InvalidNetworkId
get_network_id() -> Option — read accessor
payment_executor contract (contracts/payment_executor/src/lib.rs)
New DeploymentError enum (AlreadyInitialized = 1, DuplicateDependency = 2, SelfReference = 3)
initialize(addresses) now returns Result<(), DeploymentError> and
rejects self-references and duplicate dependency addresses before storing
them; the initial asset allowlisting behavior is unchanged
New test crate: tests/deployment
Dedicated integration-test crate (18 tests, all passing) covering:

success paths for both contracts' initialize
every DeploymentError variant for both contracts
privacy check: the initialization event exposes only public configuration
addresses — never salary amounts, commitments, or other private values
network-id lifecycle: set/get, admin gating, one-time semantics, length
limits, event emission
Test-suite repairs (pre-existing failures verified at HEAD)
These tests were failing on main but were previously masked by workspace
compile breakage:

payment_executor: stale event-count assertions updated for the
TreasuryAssetAllowedUpdated event (issue #175)
payment_executor: implemented the per-period payment_count increment in
execute_payment (invariant I-8 documented it; the field was never
incremented)
recovery_tests: two tests assumed partial batch state survives an errored
call — impossible under Soroban's atomic execution. Rewritten to assert
full rollback plus individual-payment recovery
treasury_authorization_tests: the mismatched-treasury test expected a
panic that the placeholder token (which intentionally omits
from.require_auth()) can never produce. Converted to a test pinning the
current behavior so swapping in a real SEP-41 token surfaces here
migration_tests: fixed fixture drift (zero ledger timestamp, registry
commitment not synced on rotation, hardcoded company ID, unclosed period
blocking new periods, migration reads of non-existent reduced-fixture
state)
integration_tests: fixed e2e event-topic assertion to handle both topic
layouts (payroll-domain events use ("payroll", ); other emitters
put the name first)
Lint debt cleanup so cargo clippy --workspace --all-targets -D warnings
passes (needless borrows in audit_module, dead code, unused imports,
fixtures lints)
Docs
docs/deployment.md: new "Deployment Parameter Validation" section with
the rule table, error codes, and network-id operator steps
docs/sdk-interface-spec.md: DeploymentError reference table, updated
initialize entries, documented set_network_id / get_network_id
docs/deployment-verification.md,
docs/interop/client-fallback-behavior.md: replaced stale "panics with
Already initialized" references with the typed errors
Privacy considerations
No private data is exposed: initialization events carry only public
configuration addresses, and the network identifier is an operator-chosen
public label. Covered by a dedicated test
(dp_initialized_event_exposes_only_public_config).

Testing
cargo fmt --all -- --check # clean
cargo clippy --workspace --all-targets -D warnings # clean
cargo test --workspace # 310 passed, 0 failed
(cli excluded locally: openssl-sys cannot build in this environment without
pkg-config/OpenSSL; it builds in CI.)

[github-actions]

@Stanley-Owoh this PR currently has merge conflicts.

Please resolve the conflicts before it can be merged automatically.