feat(search): add session-backed search filters

[Microck]

Summary

• add runtime search filters to kagi search and kagi batch
• keep plain search behavior intact while routing filtered searches through the session-backed web product
• refresh search docs and demo to cover the new filter surface

Implementation

• add --region, --time, --from-date, --to-date, --order, --verbatim, --personalized, and --no-personalized
• validate date formats and reject incompatible combinations like --time with explicit date ranges
• keep plain base search on the current path, but require the session-backed web route for lenses or runtime filters
• normalize full Session Link URLs when loading session auth from env or config

Docs and Demo

• update the search command reference, README, auth matrix, coverage, error reference, authentication guide, quickstart, troubleshooting, and API coverage docs
• refresh scripts/demo-search.sh
• update the search GIF assets

Verification

• cargo fmt --all --check
• cargo test
• cargo clippy --all-targets --all-features -- -D warnings
• cargo build
• ./target/debug/kagi auth check
• live plain search
• live filtered search with --region, --time, --order, --verbatim, and --no-personalized
• live batch search with date filters
• invalid --time plus date-range rejection
• invalid nonexistent date rejection
• inverted date-range rejection
• invalid session-token rejection for filtered search
• Session Link URL normalization verified through an env override
• ./scripts/demo-search.sh

Notes

• search filters are session-backed because the public Search API only supports plain base search
• safe_search remains an account setting, not a per-request CLI runtime flag in this PR